combinatorics/permutations: Corrected doctests and added docstrings for ascents and descents.
combinatorics/permutations: Corrected doctests and added
docstrings for ascents and descents.

Signed-off-by: Saptarshi Mandal <13ec3c7bab52575f3a0cda6406c76269cc13b041@gmail.com>

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