reshuffle pluginmanager methods and add some docstrings.
reshuffle pluginmanager methods and add some docstrings.

--HG--
branch : plugin_no_pytest

bukzor/pytest,bubenkoff/pytest,tomviner/pytest,skylarjhdownes/pytest,gabrielcnr/pytest,abusalimov/pytest,Bachmann1234/pytest,ericdill/pytest,vodik/pytest,wfxiang08/pytest,lukas-bednar/pytest,codewarrior0/pytest,ropez/pytest,markshao/pytest,wfxiang08/pytest,JonathonSonesen/pytest,JonathonSonesen/pytest,mdboom/pytest,userzimmermann/pytest,ojake/pytest,hpk42/pytest,davidszotten/pytest,gabrielcnr/pytest,mbirtwell/pytest,chillbear/pytest,vmalloc/dessert,rouge8/pytest,Bjwebb/pytest,jb098/pytest,pytest-dev/pytest,Haibo-Wang-ORG/pytest,MengJueM/pytest,jaraco/pytest,txomon/pytest,alfredodeza/pytest,Carreau/pytest,nicoddemus/pytest,nicoddemus/repo-test,icemac/pytest,tomviner/pytest,ericdill/pytest,mhils/pytest,hackebrot/pytest,Akasurde/pytest,ghostsquad/pytest,vodik/pytest,MengJueM/pytest,userzimmermann/pytest,hunse/pytest,chiller/pytest,ddboline/pytest,doordash/pytest,chiller/pytest,ropez/pytest,eli-b/pytest,mhils/pytest,oleg-alexandrov/pytest,inirudebwoy/pytest,flub/pytest,pelme/pytest,oleg-alexandrov/pytest,omarkohl/pytest,jb098/pytest,mbirtwell/pytest,tareqalayan/pytest,malinoff/pytest,Bjwebb/pytest,icemac/pytest,ghostsquad/pytest,codewarrior0/pytest,abusalimov/pytest,Carreau/pytest,chillbear/pytest,hunse/pytest,bukzor/pytest,RonnyPfannschmidt/pytest,doordash/pytest,lukas-bednar/pytest,MichaelAquilina/pytest,hpk42/pytest,rouge8/pytest,untitaker/pytest,mdboom/pytest,bubenkoff/pytest,nicoddemus/pytest,ionelmc/pytest,nicoddemus/repo-test,inirudebwoy/pytest,The-Compiler/pytest,untitaker/pytest,The-Compiler/pytest,Bachmann1234/pytest,pfctdayelise/pytest,omarkohl/pytest,takluyver/pytest,ionelmc/pytest,Haibo-Wang-ORG/pytest,ojake/pytest,tgoodlet/pytest,rmfitzpatrick/pytest,takluyver/pytest,etataurov/pytest,pelme/pytest