refactor(store/event_history): cleanup some comments
refactor(store/event_history): cleanup some comments

yudai/etcd,tangkun75/etcd,jeremyeder/etcd,giantswarm/etcd,njharman/etcd,yyljlyy/etcd,whuwxl/etcd,ajityagaty/etcd,betawaffle/etcd,wantonsolutions/dinv-etcd,yyljlyy/etcd,honeyqa/etcd,axingblog/etcd,visheshnp/etcd,pigfoot/etcd,shakefu/etcd,arthurcolle/etcd,hzy001/etcd,cockroachdb/etcd,zaphod-concur/etcd,freeloop1114/etcd,jravetch/etcd,xebitstudios/etcd,jlamillan/etcd,onlyjob/etcd,svdata/etcd,chai2010/etcd,kingland/etcd,raoofm/etcd,insequent/etcd,svdata/etcd,offscale/etcd,dalanlan/etcd,buaazp/etcd,OyTao/etcd_learning,chai2010-playground/etcd,xdlinear/etcd,iamqizhao/etcd,hongbinz/etcd,nekto0n/etcd,bdarnell/etcd,linuxcer/etcd,rnaveiras/etcd,shakefu/etcd,Yhgenomics/etcd,insionng/etcd,sebrandon1/etcd,ktateish/etcd,lumjjb/etcd,QuantiumTechnology/etcd,linuxcer/etcd,cvik/etcd,mickep76/etcd,elimisteve/etcd,fanminshi/etcd,spotify/etcd,coreos/etcd,barakmich/etcd,glensc/etcd,YuleiXiao/etcd,sofuture/etcd,es-chow/etcd,youxidev/etcd,xdlinear/etcd,zaphod-concur/etcd,honeyqa/etcd,bspline/etcd,westhood/etcd,CrazyJvm/etcd,jchauncey/etcd,gtank/etcd,mwitkow-io/etcd,hongbinz/etcd,cchamplin/etcd,iamqizhao/etcd,junxu/etcd,openedbox/etcd,insionng/etcd,shawnps/etcd,jlamillan/etcd,giantswarm/etcd,ktateish/etcd,gityf/etcd,luxas/etcd,rchicoli/etcd,swingbach/etcd,dterei/etcd,shawnps/etcd,oscarrr110/etcd,cvik/etcd,tamird/etcd,xiang90/etcd,msanterre/etcd,mgoelzer/etcd-fork2,Timer/etcd,wowsoso/etcd,swingbach/etcd,vimalk78/etcd,ylong/etcd,kingland/etcd,cvik/etcd,hongchaodeng/etcd,mwitkow/etcd,purpleidea/etcd,coreos/etcd,oscarrr110/etcd,HideoYamauchi/etcd,xueshanf/etcd,achanda/etcd,raoofm/etcd,njharman/etcd,lzbgt/etcd,crandles/etcd,yifan-gu/etcd,tguangch/etcd,pauldallen/etcd,heyitsanthony/etcd,polvi/etcd,insequent/etcd,chai2010/etcd,chipironcin/etcd,jmptrader/etcd,OyTao/etcd_learning,freeloop1114/etcd,rchicoli/etcd,gae123/etcd,QuantiumTechnology/etcd,cockroachdb/etcd,mwitkow-io/etcd,hpcloud/etcd,nkhare/etcd,chenbaihu/etcd,glevand/coreos--etcd,akauppi/etcd,StorReduce/etcd,wantonsolutions/dinv-etcd,gtank/etcd,glycerine/etcd,imzhulei/etcd,whuwxl/etcd,elimisteve/etcd,robszumski/etcd,hpcloud/etcd,HideoYamauchi/etcd,mkumatag/etcd,dnaeon/etcd,arthurcolle/etcd,joshix/etcd,CrazyJvm/etcd,StorReduce/etcd,robszumski/etcd,dannysauer/etcd,mike-lerch/etcd,purpleidea/etcd,pengzj/etcd,fanminshi/etcd,bdarnell/etcd,a-robinson/etcd,qqsun8819/etcd,tguangch/etcd,fgbreel/etcd,gityf/etcd,a-robinson/etcd,gouyang/etcd,nekto0n/etcd,sinsharat/etcd,buaazp/etcd,bluebreezecf/etcd,asim/etcd,sebrandon1/etcd,msanterre/etcd,njucslqq/etcd,xiang90/etcd,junxu/etcd,mwitkow/etcd,mqliang/etcd,gosharplite/etcd,ajityagaty/etcd,spotify/etcd,offscale/etcd,spacejam/etcd,TheHippo/etcd,hroyrh/etcd,axingblog/etcd,TheHippo/etcd,rnaveiras/etcd,devfreesg/etcd,delkyd/etcd,pengzj/etcd,visheshnp/etcd,plasticbox/etcd,gyuho/etcd,beni55/etcd,Timer/etcd,imzhulei/etcd,YuleiXiao/etcd,Yhgenomics/etcd,luxas/etcd,li-ang/etcd,xueshanf/etcd,jonboulle/etcd,qiaochao911/etcd,mgoelzer/etcd-fork2,steveeJ/etcd,barakmich/etcd,chai2010-playground/etcd,tangkun75/etcd,joshix/etcd,fasaxc/etcd,wfxiang08/etcd,xebitstudios/etcd,endocode/etcd,Eagle-X/etcd,beni55/etcd,akauppi/etcd,mkumatag/etcd,dalanlan/etcd,mkumatag/etcd,bakins/etcd,plasticbox/etcd,improbable-io/etcd,wowsoso/etcd,yudai/etcd,delkyd/etcd,kkaneda/etcd,cognusion/etcd,endocode/etcd,mitake/etcd,betawaffle/etcd,Eagle-X/etcd,siddontang/etcd,mickep76/etcd,wantonsolutions/dinv-etcd,hongchaodeng/etcd,sebschrader/etcd,jonboulle/etcd,tempbottle/etcd,chenbaihu/etcd,jefby/etcd,pauldallen/etcd,glycerine/etcd,mqliang/etcd,handsomesun/etcd,Winslett/etcd,spotify/etcd,yifan-gu/etcd,hzy001/etcd,princeqjzh/etcd,snailwalker/etcd,ajityagaty/etcd,xychu/etcd,nieanan/etcd,nkhare/etcd,westhood/etcd,glevand/coreos--etcd,snailwalker/etcd,nieanan/etcd,lorneli/etcd,ravigadde/etcd,fgbreel/etcd,li-ang/etcd,bspline/etcd,ecnahc515/etcd,yichengq/etcd,jravetch/etcd,es-chow/etcd,spotify/etcd,armstrongli/etcd,justintung/etcd,ravigadde/etcd,hroyrh/etcd,shafreeck/etcd,justintung/etcd,cognusion/etcd,gouyang/etcd,armstrongli/etcd,vimalk78/etcd,etcd-io/etcd,siddontang/etcd,Ulexus/etcd,cvik/etcd,shafreeck/etcd,sinsharat/etcd,yichengq/etcd,combk8s/etcd,sayden/etcd,bluebreezecf/etcd,lorneli/etcd,Ulexus/etcd,mqliang/etcd,wfxiang08/etcd,olark/etcd,jeremyeder/etcd,devfreesg/etcd,princeqjzh/etcd,SivagnanamCiena/etcd,sayden/etcd,glensc/etcd,csuideal/etcd,lumjjb/etcd,chipironcin/etcd,olark/etcd,mitake/etcd,jefby/etcd,xychu/etcd,youxidev/etcd,kkaneda/etcd,tempbottle/etcd,dnaeon/etcd,SivagnanamCiena/etcd,fasaxc/etcd,spacejam/etcd,gosharplite/etcd,openedbox/etcd,handsomesun/etcd,achanda/etcd,csuideal/etcd,gae123/etcd,Ulexus/etcd,dterei/etcd,mischief/etcd,onlyjob/etcd,dannysauer/etcd,fasaxc/etcd,mischief/etcd,asim/etcd,ecnahc515/etcd,steveeJ/etcd,etcd-io/etcd,qiaochao911/etcd,heyitsanthony/etcd,lzbgt/etcd,polvi/etcd,rnaveiras/etcd,cchamplin/etcd,Ulexus/etcd,sebschrader/etcd,crandles/etcd,njucslqq/etcd,ylong/etcd,bakins/etcd,improbable-io/etcd,sofuture/etcd,combk8s/etcd,tamird/etcd,Winslett/etcd,jmptrader/etcd,mike-lerch/etcd,etcd-io/etcd,jchauncey/etcd,gyuho/etcd,qqsun8819/etcd