Add doctests for all user-facing methods.
Add doctests for all user-facing methods.

I suppose that some of the docstrings have now become a bit redundant; I
don't think that's a problem at all with docstrings, however.

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