Consistency w/ 0s in mechanics
Consistency w/ 0s in mechanics

Previously, there were inconsistencies in mechanics.essential, with some
methods using S(0) to form empty Vectors and others using an empty Vector
(Vector([])). This has now been corrected to use empty vectors only. The same
is true for the Dyadic class.

rahuldan/sympy,vipulroxx/sympy,rahuldan/sympy,cswiercz/sympy,AunShiLord/sympy,lidavidm/sympy,farhaanbukhsh/sympy,ahhda/sympy,chaffra/sympy,shikil/sympy,Gadal/sympy,hrashk/sympy,mcdaniel67/sympy,MechCoder/sympy,postvakje/sympy,Shaswat27/sympy,AunShiLord/sympy,iamutkarshtiwari/sympy,vipulroxx/sympy,meghana1995/sympy,moble/sympy,kmacinnis/sympy,rahuldan/sympy,sampadsaha5/sympy,aktech/sympy,kevalds51/sympy,AkademieOlympia/sympy,liangjiaxing/sympy,pandeyadarsh/sympy,debugger22/sympy,shipci/sympy,jbbskinny/sympy,jamesblunt/sympy,shipci/sympy,Arafatk/sympy,kumarkrishna/sympy,maniteja123/sympy,AkademieOlympia/sympy,iamutkarshtiwari/sympy,sunny94/temp,bukzor/sympy,cccfran/sympy,atsao72/sympy,ChristinaZografou/sympy,aktech/sympy,hargup/sympy,aktech/sympy,hrashk/sympy,garvitr/sympy,skidzo/sympy,shikil/sympy,souravsingh/sympy,Curious72/sympy,liangjiaxing/sympy,mafiya69/sympy,MechCoder/sympy,atreyv/sympy,Davidjohnwilson/sympy,pbrady/sympy,postvakje/sympy,diofant/diofant,jerli/sympy,wyom/sympy,sahilshekhawat/sympy,emon10005/sympy,MridulS/sympy,jaimahajan1997/sympy,VaibhavAgarwalVA/sympy,Mitchkoens/sympy,jbbskinny/sympy,ChristinaZografou/sympy,Gadal/sympy,beni55/sympy,souravsingh/sympy,madan96/sympy,abloomston/sympy,sunny94/temp,jamesblunt/sympy,kumarkrishna/sympy,oliverlee/sympy,beni55/sympy,oliverlee/sympy,jamesblunt/sympy,pbrady/sympy,VaibhavAgarwalVA/sympy,sahilshekhawat/sympy,Arafatk/sympy,drufat/sympy,kaichogami/sympy,abhiii5459/sympy,asm666/sympy,lidavidm/sympy,mafiya69/sympy,farhaanbukhsh/sympy,atreyv/sympy,lindsayad/sympy,abhiii5459/sympy,Curious72/sympy,postvakje/sympy,wanglongqi/sympy,debugger22/sympy,Shaswat27/sympy,chaffra/sympy,beni55/sympy,MridulS/sympy,VaibhavAgarwalVA/sympy,Vishluck/sympy,madan96/sympy,pandeyadarsh/sympy,atreyv/sympy,wanglongqi/sympy,drufat/sympy,bukzor/sympy,hargup/sympy,sampadsaha5/sympy,AkademieOlympia/sympy,Sumith1896/sympy,jaimahajan1997/sympy,skidzo/sympy,meghana1995/sympy,yashsharan/sympy,grevutiu-gabriel/sympy,atsao72/sympy,Titan-C/sympy,moble/sympy,emon10005/sympy,atsao72/sympy,cccfran/sympy,Shaswat27/sympy,toolforger/sympy,mcdaniel67/sympy,Designist/sympy,Vishluck/sympy,jbbskinny/sympy,yashsharan/sympy,shipci/sympy,Curious72/sympy,toolforger/sympy,vipulroxx/sympy,maniteja123/sympy,kevalds51/sympy,souravsingh/sympy,maniteja123/sympy,pbrady/sympy,Designist/sympy,AunShiLord/sympy,dqnykamp/sympy,abloomston/sympy,jerli/sympy,emon10005/sympy,jerli/sympy,wyom/sympy,oliverlee/sympy,Sumith1896/sympy,wyom/sympy,liangjiaxing/sympy,MechCoder/sympy,kaichogami/sympy,chaffra/sympy,MridulS/sympy,Mitchkoens/sympy,ahhda/sympy,hrashk/sympy,yukoba/sympy,bukzor/sympy,ChristinaZografou/sympy,Gadal/sympy,Designist/sympy,cswiercz/sympy,moble/sympy,yukoba/sympy,asm666/sympy,hargup/sympy,debugger22/sympy,skirpichev/omg,Titan-C/sympy,mafiya69/sympy,kaushik94/sympy,drufat/sympy,cccfran/sympy,saurabhjn76/sympy,lindsayad/sympy,kumarkrishna/sympy,sampadsaha5/sympy,lidavidm/sympy,Davidjohnwilson/sympy,kmacinnis/sympy,wanglongqi/sympy,Titan-C/sympy,abhiii5459/sympy,Mitchkoens/sympy,kaushik94/sympy,sahmed95/sympy,yukoba/sympy,ga7g08/sympy,Vishluck/sympy,shikil/sympy,Arafatk/sympy,cswiercz/sympy,saurabhjn76/sympy,lindsayad/sympy,dqnykamp/sympy,garvitr/sympy,Sumith1896/sympy,jaimahajan1997/sympy,skidzo/sympy,kaichogami/sympy,meghana1995/sympy,abloomston/sympy,iamutkarshtiwari/sympy,sahmed95/sympy,grevutiu-gabriel/sympy,sunny94/temp,garvitr/sympy,yashsharan/sympy,kevalds51/sympy,mcdaniel67/sympy,asm666/sympy,kaushik94/sympy,ga7g08/sympy,sahmed95/sympy,toolforger/sympy,kmacinnis/sympy,madan96/sympy,saurabhjn76/sympy,Davidjohnwilson/sympy,sahilshekhawat/sympy,grevutiu-gabriel/sympy,dqnykamp/sympy,farhaanbukhsh/sympy,pandeyadarsh/sympy,ahhda/sympy,ga7g08/sympy