Add doctests to all functions in sympy/polys/densearith.py
Add doctests to all functions in sympy/polys/densearith.py

Signed-off-by: Mateusz Paprocki <4e51c28eba28c1534bcc4a6bd2cccd314d8bf749@gmail.com>

Mitchkoens/sympy,oliverlee/sympy,kumarkrishna/sympy,asm666/sympy,pandeyadarsh/sympy,madan96/sympy,debugger22/sympy,yukoba/sympy,aktech/sympy,Arafatk/sympy,maniteja123/sympy,atsao72/sympy,meghana1995/sympy,Titan-C/sympy,madan96/sympy,mafiya69/sympy,maniteja123/sympy,Davidjohnwilson/sympy,MridulS/sympy,farhaanbukhsh/sympy,oliverlee/sympy,sahmed95/sympy,oliverlee/sympy,yukoba/sympy,cswiercz/sympy,souravsingh/sympy,MridulS/sympy,hrashk/sympy,lindsayad/sympy,Arafatk/sympy,jerli/sympy,souravsingh/sympy,Arafatk/sympy,Designist/sympy,skidzo/sympy,maniteja123/sympy,aktech/sympy,mcdaniel67/sympy,Sumith1896/sympy,asm666/sympy,yukoba/sympy,saurabhjn76/sympy,liangjiaxing/sympy,shipci/sympy,postvakje/sympy,AunShiLord/sympy,garvitr/sympy,sunny94/temp,kumarkrishna/sympy,garvitr/sympy,jbbskinny/sympy,pernici/sympy,toolforger/sympy,kmacinnis/sympy,emon10005/sympy,cccfran/sympy,wyom/sympy,sahilshekhawat/sympy,farhaanbukhsh/sympy,aktech/sympy,meghana1995/sympy,drufat/sympy,jaimahajan1997/sympy,hargup/sympy,mcdaniel67/sympy,vipulroxx/sympy,madan96/sympy,Titan-C/sympy,jamesblunt/sympy,AkademieOlympia/sympy,shikil/sympy,moble/sympy,beni55/sympy,abloomston/sympy,bukzor/sympy,shipci/sympy,hrashk/sympy,mafiya69/sympy,yashsharan/sympy,cccfran/sympy,wanglongqi/sympy,Gadal/sympy,jerli/sympy,yashsharan/sympy,MechCoder/sympy,sahilshekhawat/sympy,lidavidm/sympy,atreyv/sympy,beni55/sympy,souravsingh/sympy,abhiii5459/sympy,Mitchkoens/sympy,emon10005/sympy,kaushik94/sympy,debugger22/sympy,atreyv/sympy,toolforger/sympy,Vishluck/sympy,kevalds51/sympy,flacjacket/sympy,Mitchkoens/sympy,ChristinaZografou/sympy,Gadal/sympy,garvitr/sympy,jbbskinny/sympy,cswiercz/sympy,VaibhavAgarwalVA/sympy,kaushik94/sympy,moble/sympy,jerli/sympy,Sumith1896/sympy,pbrady/sympy,amitjamadagni/sympy,minrk/sympy,yashsharan/sympy,hrashk/sympy,atsao72/sympy,vipulroxx/sympy,abhiii5459/sympy,cccfran/sympy,iamutkarshtiwari/sympy,ga7g08/sympy,shikil/sympy,dqnykamp/sympy,srjoglekar246/sympy,abhiii5459/sympy,Shaswat27/sympy,sunny94/temp,pandeyadarsh/sympy,AkademieOlympia/sympy,sahilshekhawat/sympy,minrk/sympy,wanglongqi/sympy,iamutkarshtiwari/sympy,ga7g08/sympy,AkademieOlympia/sympy,kevalds51/sympy,MechCoder/sympy,debugger22/sympy,ga7g08/sympy,lidavidm/sympy,cswiercz/sympy,abloomston/sympy,sampadsaha5/sympy,vipulroxx/sympy,kaichogami/sympy,Curious72/sympy,lidavidm/sympy,liangjiaxing/sympy,saurabhjn76/sympy,jamesblunt/sympy,sahmed95/sympy,diofant/diofant,wyom/sympy,atsao72/sympy,shipci/sympy,bukzor/sympy,Designist/sympy,Shaswat27/sympy,saurabhjn76/sympy,postvakje/sympy,liangjiaxing/sympy,rahuldan/sympy,kaushik94/sympy,ahhda/sympy,MridulS/sympy,sunny94/temp,grevutiu-gabriel/sympy,dqnykamp/sympy,hargup/sympy,Davidjohnwilson/sympy,asm666/sympy,jamesblunt/sympy,sahmed95/sympy,skirpichev/omg,rahuldan/sympy,lindsayad/sympy,postvakje/sympy,kmacinnis/sympy,jaimahajan1997/sympy,kaichogami/sympy,chaffra/sympy,Curious72/sympy,ahhda/sympy,shikil/sympy,grevutiu-gabriel/sympy,ahhda/sympy,atreyv/sympy,grevutiu-gabriel/sympy,kevalds51/sympy,wanglongqi/sympy,Titan-C/sympy,Davidjohnwilson/sympy,farhaanbukhsh/sympy,skidzo/sympy,sampadsaha5/sympy,drufat/sympy,mafiya69/sympy,VaibhavAgarwalVA/sympy,abloomston/sympy,pbrady/sympy,Sumith1896/sympy,lindsayad/sympy,sampadsaha5/sympy,Curious72/sympy,chaffra/sympy,kumarkrishna/sympy,jbbskinny/sympy,moble/sympy,amitjamadagni/sympy,iamutkarshtiwari/sympy,dqnykamp/sympy,beni55/sympy,rahuldan/sympy,Vishluck/sympy,toolforger/sympy,skidzo/sympy,meghana1995/sympy,Gadal/sympy,emon10005/sympy,VaibhavAgarwalVA/sympy,Vishluck/sympy,AunShiLord/sympy,pandeyadarsh/sympy,kmacinnis/sympy,ChristinaZografou/sympy,pbrady/sympy,ChristinaZografou/sympy,drufat/sympy,Shaswat27/sympy,chaffra/sympy,MechCoder/sympy,mcdaniel67/sympy,AunShiLord/sympy,kaichogami/sympy,Designist/sympy,bukzor/sympy,hargup/sympy,jaimahajan1997/sympy,wyom/sympy