With the deprecation of class_inheritable_accessor, the fields module needed a rework.
With the deprecation of class_inheritable_accessor, the fields module
needed a rework.

- Now when inherited the fields from the parent will be copied to the
  child, mimicking the old behaviour.

- Fixes #508.

slbug/mongoid,hbakhtiyor/mongoid,goshakkk/mongoid,sserdyuk/mongoid,Codas/mongoid,flyerhzm/mongoid,bigbenli/mongoid,wuboy0307/mongoid,mash-ltd/mongoid,atomical/mongoid,lawrencecurtis/mongoid,paulrosania/mongoid,akirasosa/mongoid,aileron/mongoid,nickhoffman/mongoid,Numerico/mongoid,HeeL/mongoid-1,mitijain123/mongoid,Speakol/mongoid,razum2um/mongoid,brynary/mongoid,DouweM/mongoid,zenjoy/mongoid,xentek/mongoid,ahoward/mongoid,sikachu/mongoid,drobune/mongoid,Winslett/mongoid,grossws/mongoid,gregory-m/mongoid,idesaku/mongoid,itbakery/mongoid,sevos/mongoid,alex-klepa/mongoid,kentaroi/mongoid,derekharmel/mongoid,alexandru-calinoiu/mongoid,abezzub/mongoid,leedo/mongoid,notxarb/mongoid,cavneb/mongoid,neerfri/mongoid,akm/mongoid,jonasschneider/mongoid,dlt/mongoid,dannguyen/mongoid,dakatsuka/mongoid,lowang/mongoid,semaperepelitsa/mongoid,tvon/mongoid,asaaki/mongoid,socialreferral/mongoid,77Agency/mongoid,codedmart/mongoid,MSNexploder/mongoid,priyaaank/mongoid,christiannelson/mongoid,kay-kim/mongoid,florent/mongoid,estolfo/mongoid,adyard/mongoid,gullitmiranda/mongoid,rymai/mongoid,dbkbali/mongoid,irakli-janiashvili/mongoid,hookercookerman/mongoid,sideci-sample/sideci-sample-mongoid,shingara/mongoid,nullstyle/mongoid,Houdini/mongoid,demarque/mongoid,envylabs/mongoid,derekharmel/mongoid,rubrikkfabrikken/mongoid,robwil/mongoid,KoanHealth/mongoid,haihappen/mongoid,EqualMedia/mongoid,uranazo/mongoid,tzar/mongoid,aagrawal2001/mongoid,dnd/mongoid,rafaelgaspar/mongoid,cao7113/mongoid,crealytics/mongoid,stellard/mongoid,robinst/mongoid,glebtv/mongoid,eljojo/mongoid,karmakaze/mongoid,asaaki/mongoid,FestivalBobcats/mongoid,rinmu/mongoid,bencrouse/mongoid,sevos/mongoid,jamesalmond/mongoid,CIRCUITLLC/mongoid,aleksclark/mongoid,bjori/mongoid,pkieltyka/mongoid,hfwang/mongoid,nicolasblanco/mongoid,hbakhtiyor/mongoid,estolfo/mongoid,parov/mongoid,SumeruSoftware/mongoid,sporkd/mongoid,apptentive-engineering/mongoid,anuprit/mongoid,cleishm/mongoid,eddanger/mongoid,dlt/mongoid,4pcbr/mongoid,cmartyn/mongoid,johnnyshields/mongoid,nextmat/mongoid,hashrocketeer/mongoid,balauru/mongoid,canavese/mongoid,aagrawal2001/mongoid,mongoid/mongoid,gicappa/mongoid,krasnoukhov/mongoid,outoftime/mongoid,tzar/mongoid,elia/mongoid,jmaicher/mongoid,derickbailey/mongoid,KoanHealth/mongoid,colinyoung/mongoid,marcweil/mongoid,ealdent/mongoid,mzsanford/mongoid,env0der/mongoid,crealytics/mongoid,matadon/mongoid,sukeerthiadiga/mongoid,HRNewMedia/mongoid,grossws/mongoid,hubertlepicki/mongoid,kuadrosx/mongoid,flada-auxv/mongoid,narutosanjiv/mongoid,fbernier/mongoid,ErisExchange/mongoid,astjohn/mongoid,Azzurrio/mongoid,mulder/mongoid,PerfectMemory/mongoid,camallen/mongoid,lucasas/mongoid,herimedia/mongoid,skyeagle/mongoid,FestivalBobcats/mongoid,joneslee85/mongoid,mschulkind/mongoid,brettgoulder/mongoid-1,zBMNForks/mongoid,tagliala/mongoid,maxd/mongoid,mattconnolly/mongoid,neerfri/mongoid,Azzurrio/mongoid,leedo/mongoid,rubrikkfabrikken/mongoid,joshsoftware/mongoid,tombruijn/mongoid,cncolder/mongoid,stnguyen/mongoid,ErisExchange/mongoid,hadees/mongoid,caiofilipini/mongoid,afeld/mongoid,javmorin/mongoid,fortnightlabs/mongoid,parov/mongoid,loginx/mongoid,ebeigarts/mongoid,kevinmarvin/mongoid,korishev/mongoid,arunagw/mongoid,zenjoy/mongoid,jasonsydes/mongoid,crowdtap/mongoid,leemhenson/mongoid,notxarb/mongoid,stevebartholomew/mongoid,dnd/mongoid,matbox/mongoid,amw/mongoid,icambron/mongoid,cmpolis/mongoid,robwil/mongoid,bdmac/mongoid,ahoward/mongoid,teaforthecat/mongoid,etomic/mongoid,EqualMedia/mongoid,Exoth/mongoid,tolsen/mongoid,captain-lucas/mongoid,rosylilly/mongoid,kay-kim/mongoid,joneslee85/mongoid,luxerama/mongoid,skiz/mongoid,nviennot/mongoid,abscondment/mongoid,grimen/mongoid,potatosalad/mongoid,hubertlepicki/mongoid,jordoh/mongoid,alexandru-calinoiu/mongoid,sideci-sample/sideci-sample-mongoid,jordelver/mongoid,mhs/mongoid,cao7113/mongoid,akreiling/mongoid,jakcharlton/mongoid,razum2um/mongoid,jpfuentes2/mongoid,cpuguy83/mongoid,akirasosa/mongoid,ono/mongoid,sikachu/mongoid,marcweil/mongoid,ElvinEfendi/mongoid,afeld/mongoid,freerange/mongoid,ches/mongoid,Tickaroo/mongoid2,charliehq/mongoid,lackac/mongoid,kryzhovnik/mongoid,kostyantyn/mongoid,hfwang/mongoid,johnny-miyake/mongoid,jetthoughts/mongoid,flada-auxv/mongoid,hadees/mongoid,akm/mongoid,alexrothenberg/mongoid,blt04/mongoid,capnregex/mongoid,britto/mongoid,jakcharlton/mongoid,freerange/mongoid,jasl/mongoid,trmmy/mongoid,nextmat/mongoid,bjori/mongoid,toppan-forms/mongoid,bearded/mongoid,pkieltyka/mongoid,bencrouse/mongoid,manuelmorales/mongoid,chetan/mongoid,blackxored/mongoid,jeffreyiacono/mongoid,uniiverse/mongoid,charliehq/mongoid,tengine/mongoid,greggroth/mongoid,lawrencecurtis/mongoid,jseibert/mongoid,genexp/mongoid,mikerobe/mongoid,atomical/mongoid,iboard/mongoid-1,xinuc/mongoid,gregmolnar/mongoid,moretea/mongoid,romanbsd/mongoid,kcdragon/mongoid,fredjean/mongoid,yuuna/mongoid,shotoso/mongoid,jetheredge/mongoid,hashrocketeer/mongoid,florent/mongoid,rinmu/mongoid,lowang/mongoid,xentek/mongoid,LastStar/mongoid,ginty/mongoid,cavneb/mongoid,alexrothenberg/mongoid,trmmy/mongoid,evansagge/mongoid,socialreferral/mongoid,simi/mongoid,mongoid/mongoid,drobune/mongoid,Sharevari-Inc/mongoid,Winslett/mongoid,nullstyle/mongoid,demarque/mongoid,jiren/mongoid,Zhomart/mongoid,spiegela/mongoid,abscondment/mongoid,travis-repos/mongoid,travis-repos/mongoid,nickhoffman/mongoid,moretea/mongoid,uranazo/mongoid,dferdian/mongoid,mhs/mongoid,nusco/mongoid,xinuc/mongoid,MSNexploder/mongoid,snapfish-soma/mongoid,wuboy0307/mongoid,sepastian/mongoid,zaithottakath/mongoid,javmorin/mongoid,potatosalad/mongoid,SumeruSoftware/mongoid,kslazarev/mongoid,rogerz42892/mongoid,gregmolnar/mongoid,Spaceghost/mongoid,hookercookerman/mongoid,tetsuo692/mongoid,derickbailey/mongoid,byroot/mongoid,karmakaze/mongoid,praecipula/mongoid,stnguyen/mongoid,brettgoulder/mongoid-1,genexp/mongoid,stellard/mongoid,itbakery/mongoid,shotoso/mongoid,jstrocel/mongoid,Flameeyes/mongoid,joshleitzel/mongoid,mattconnolly/mongoid,nviennot/mongoid,cmpolis/mongoid,abezzub/mongoid,toppan-forms/mongoid,mehowte/mongoid,theirishpenguin/mongoid,maxd/mongoid,anuprit/mongoid,aileron/mongoid,camallen/mongoid,ganlron/mongoid,stevebartholomew/mongoid,kuadrosx/mongoid,Empact/mongoid,hxx/mongoid,mongodb/mongoid,aj0strow/mongoid,sserdyuk/mongoid,skippy/mongoid,tetsuo692/mongoid,codedmart/mongoid,mzsanford/mongoid,absperf/mongoid,andreychernih/mongoid,malditogeek/mongoid,cgriego/mongoid,bigbenli/mongoid,zBMNForks/mongoid,etomic/mongoid,ches/mongoid,sujal/mongoid,iGoDigital-LLC/mongoid,X0nic/mongoid,tvon/mongoid,zanker/mongoid,simi/mongoid,captain-lucas/mongoid,tanordheim/mongoid,mitio/mongoid,christiannelson/mongoid,asantamar/mongoid,eljojo/mongoid,britto/mongoid,albus522/mongoid,kslazarev/mongoid,luxerama/mongoid,Welovroi/mongoid,idesaku/mongoid,i0rek/mongoid,iamnader/mongoid-2,joshleitzel/mongoid,incorvia/mongoid,JonRowe/mongoid,gicappa/mongoid,praecipula/mongoid,PerfectMemory/mongoid,adyard/mongoid,piotrj/mongoid,tanordheim/mongoid,jpfuentes2/mongoid,krasnoukhov/mongoid,incorvia/mongoid,icambron/mongoid,blackxored/mongoid,mysociety/mongoid,codedogfish/mongoid,zanker/mongoid,skiz/mongoid,franc/mongoid,cpuguy83/mongoid,outoftime/mongoid,ebeigarts/mongoid,77Agency/mongoid,flexoid/mongoid,mysociety/mongoid,mathieuravaux/mongoid,kuruma-gs/mongoid,subhashb/mongoid,infiverve/mongoid,kostyantyn/mongoid,kevinmarvin/mongoid,chriseppstein/mongoid,mschulkind/mongoid,ryanong/mongoid,shingara/mongoid,bobbytables/mongoid,hxx/mongoid,mongodb/mongoid,Subskii/mongoid,glebtv/mongoid,canvas-drw/mongoid,canvas-drw/mongoid,jim/mongoid,johnny-miyake/mongoid,imomoisoft/mongoid,kentaroi/mongoid,mgartner/mongoid,teaforthecat/mongoid,paulrosania/mongoid,infiverve/mongoid,janroesner/mongoid,DanielVartanov/mongoid,rafaelgaspar/mongoid,manuelmorales/mongoid,ryanong/mongoid,jeyb/mongoid,goshakkk/mongoid,jasl/mongoid,kayakyakr/mongoid,ElvinEfendi/mongoid,Aupajo/mongoid-1,mgartner/mongoid,bearded/mongoid,corpgovrisk/mongoid,narutosanjiv/mongoid,uniiverse/mongoid,balauru/mongoid,bdmac/mongoid,500px/mongoid,jim/mongoid,drfeelngood/mongoid,crowdtap/mongoid,Numerico/mongoid,imomoisoft/mongoid,nagachika/mongoid,jonhyman/mongoid,mulder/mongoid,manikandan-kandasamy/mongoid,schnittchen/mongoid,nfo/mongoid,voldy/mongoid,fujimura/mongoid,tricknotes/mongoid,nagachika/mongoid,drfeelngood/mongoid,rmm5t/mongoid,msaffitz/mongoid,niedhui/mongoid,dbkbali/mongoid,rosylilly/mongoid,justinko/mongoid,johnnyshields/mongoid,leozhang37/mongoid,mgolovnia/mongoid,haihappen/mongoid,jonhyman/mongoid,Welovroi/mongoid,jtescher/mongoid,nfo/mongoid,dcu/mongoid,gregory-m/mongoid,envylabs/mongoid,jmaicher/mongoid,Shop2market/mongoid,evendis/mongoid,rafaelfranca/mongoid,flyerhzm/mongoid,slbug/mongoid,rmm5t/mongoid,LastStar/mongoid,DanielVartanov/mongoid,malditogeek/mongoid,jetthoughts/mongoid,fbernier/mongoid,rebelhold/mongoid,matbox/mongoid,cmartyn/mongoid,jeyb/mongoid,arnkorty/mongoid,amw/mongoid,kryzhovnik/mongoid,dannguyen/mongoid,X0nic/mongoid,ealdent/mongoid,CIRCUITLLC/mongoid,flexoid/mongoid,chetan/mongoid,rafaelfranca/mongoid,dblock/mongoid,mash-ltd/mongoid,MadRabbit/mongoid,voldy/mongoid,mathieuravaux/mongoid,joelcogen/mongoid,aj0strow/mongoid,Sharevari-Inc/mongoid,likealittle/mongoid,joelcogen/mongoid,skippy/mongoid,joshsoftware/mongoid,arnkorty/mongoid,lucasas/mongoid,spiegela/mongoid,mitijain123/mongoid,getaroom/mongoid,bobbytables/mongoid,andreychernih/mongoid,ginty/mongoid,jordelver/mongoid,justinko/mongoid,koraktor/mongoid,dustinwatson/mongoid,mongodb/mongoid,caiofilipini/mongoid,canavese/mongoid,500px/mongoid,asantamar/mongoid,greggroth/mongoid,kayakyakr/mongoid,jstrocel/mongoid,cleishm/mongoid,evansagge/mongoid,dsachitano/mongoid,jtescher/mongoid,Spaceghost/mongoid,aleksclark/mongoid,arunagw/mongoid,iGoDigital-LLC/mongoid,Exoth/mongoid,jamesalmond/mongoid,wyattisimo/mongoid,dsachitano/mongoid,jordoh/mongoid,jbrien/mongoid,chriseppstein/mongoid,kcdragon/mongoid,corpgovrisk/mongoid,ganlron/mongoid,jseibert/mongoid,timgluz/mongoid,msaffitz/mongoid,timgluz/mongoid,sukeerthiadiga/mongoid,irakli-janiashvili/mongoid,apptentive-engineering/mongoid,brynary/mongoid,tolsen/mongoid,sporkd/mongoid,rogerz42892/mongoid,Subskii/mongoid,dcu/mongoid,Codas/mongoid,fortnightlabs/mongoid,sivagollapalli/mongoid,Zhomart/mongoid,tricknotes/mongoid,railsjedi/mongoid,sivagollapalli/mongoid,evendis/mongoid,tagliala/mongoid,mikerobe/mongoid,subhashb/mongoid,fredjean/mongoid,jeffreyiacono/mongoid,HeeL/mongoid-1,rpocklin/mongoid,herimedia/mongoid,elia/mongoid,robotmay/mongoid,cncolder/mongoid,sepastian/mongoid,akreiling/mongoid,gullitmiranda/mongoid,4pcbr/mongoid,colinyoung/mongoid,wyattisimo/mongoid,janroesner/mongoid,korishev/mongoid,dustinwatson/mongoid,Speakol/mongoid,cgriego/mongoid,eddanger/mongoid,jbrien/mongoid,mehowte/mongoid,dferdian/mongoid,kuruma-gs/mongoid,rpocklin/mongoid,tombruijn/mongoid,nusco/mongoid,niedhui/mongoid,JonRowe/mongoid,codedogfish/mongoid,cjab/mongoid,lackac/mongoid,railsjedi/mongoid,matsimitsu/mongoid,franc/mongoid,matsimitsu/mongoid,yuuna/mongoid,zaithottakath/mongoid,manikandan-kandasamy/mongoid