MAINT: stats: document the calling convention of distributions .expect method
MAINT: stats: document the calling convention of distributions .expect method

Addresses gh-4858

andyfaff/scipy,gertingold/scipy,aarchiba/scipy,pschella/scipy,jor-/scipy,Shaswat27/scipy,person142/scipy,nonhermitian/scipy,vigna/scipy,Stefan-Endres/scipy,Newman101/scipy,zerothi/scipy,matthewalbani/scipy,behzadnouri/scipy,Newman101/scipy,grlee77/scipy,josephcslater/scipy,lhilt/scipy,pbrod/scipy,gfyoung/scipy,scipy/scipy,andyfaff/scipy,Stefan-Endres/scipy,perimosocordiae/scipy,niknow/scipy,vigna/scipy,aeklant/scipy,jamestwebber/scipy,apbard/scipy,arokem/scipy,vigna/scipy,niknow/scipy,aarchiba/scipy,bkendzior/scipy,endolith/scipy,WarrenWeckesser/scipy,befelix/scipy,WarrenWeckesser/scipy,maniteja123/scipy,dominicelse/scipy,anielsen001/scipy,befelix/scipy,rgommers/scipy,sriki18/scipy,Stefan-Endres/scipy,matthew-brett/scipy,pyramania/scipy,grlee77/scipy,Stefan-Endres/scipy,niknow/scipy,rgommers/scipy,apbard/scipy,haudren/scipy,nonhermitian/scipy,andyfaff/scipy,matthew-brett/scipy,pyramania/scipy,gertingold/scipy,chatcannon/scipy,mdhaber/scipy,matthew-brett/scipy,gdooper/scipy,person142/scipy,pschella/scipy,matthewalbani/scipy,mikebenfield/scipy,person142/scipy,person142/scipy,vigna/scipy,gfyoung/scipy,chatcannon/scipy,behzadnouri/scipy,kleskjr/scipy,Newman101/scipy,behzadnouri/scipy,gfyoung/scipy,perimosocordiae/scipy,jakevdp/scipy,e-q/scipy,WarrenWeckesser/scipy,nmayorov/scipy,vigna/scipy,jamestwebber/scipy,dominicelse/scipy,argriffing/scipy,ilayn/scipy,zerothi/scipy,andyfaff/scipy,befelix/scipy,ilayn/scipy,woodscn/scipy,jjhelmus/scipy,lhilt/scipy,endolith/scipy,jamestwebber/scipy,tylerjereddy/scipy,person142/scipy,anntzer/scipy,andyfaff/scipy,grlee77/scipy,sriki18/scipy,pyramania/scipy,Eric89GXL/scipy,Shaswat27/scipy,zerothi/scipy,nmayorov/scipy,rgommers/scipy,larsmans/scipy,anielsen001/scipy,pschella/scipy,dominicelse/scipy,jjhelmus/scipy,pizzathief/scipy,rgommers/scipy,gfyoung/scipy,andyfaff/scipy,kleskjr/scipy,matthew-brett/scipy,lhilt/scipy,endolith/scipy,chatcannon/scipy,jor-/scipy,pbrod/scipy,matthewalbani/scipy,aarchiba/scipy,dominicelse/scipy,endolith/scipy,Shaswat27/scipy,ilayn/scipy,mikebenfield/scipy,chatcannon/scipy,pizzathief/scipy,maniteja123/scipy,surhudm/scipy,woodscn/scipy,behzadnouri/scipy,jjhelmus/scipy,endolith/scipy,chatcannon/scipy,Eric89GXL/scipy,nonhermitian/scipy,pbrod/scipy,jor-/scipy,kleskjr/scipy,matthewalbani/scipy,lhilt/scipy,woodscn/scipy,aeklant/scipy,dominicelse/scipy,argriffing/scipy,grlee77/scipy,bkendzior/scipy,scipy/scipy,ilayn/scipy,arokem/scipy,surhudm/scipy,woodscn/scipy,scipy/scipy,ilayn/scipy,tylerjereddy/scipy,pizzathief/scipy,sriki18/scipy,pizzathief/scipy,gfyoung/scipy,Gillu13/scipy,woodscn/scipy,gertingold/scipy,perimosocordiae/scipy,sriki18/scipy,chatcannon/scipy,pschella/scipy,jjhelmus/scipy,Stefan-Endres/scipy,anntzer/scipy,tylerjereddy/scipy,gertingold/scipy,arokem/scipy,scipy/scipy,mdhaber/scipy,zerothi/scipy,josephcslater/scipy,surhudm/scipy,Shaswat27/scipy,e-q/scipy,jamestwebber/scipy,sriki18/scipy,jakevdp/scipy,argriffing/scipy,mdhaber/scipy,Gillu13/scipy,WarrenWeckesser/scipy,nmayorov/scipy,mikebenfield/scipy,behzadnouri/scipy,Shaswat27/scipy,apbard/scipy,befelix/scipy,nmayorov/scipy,surhudm/scipy,kalvdans/scipy,haudren/scipy,anielsen001/scipy,kalvdans/scipy,mdhaber/scipy,gdooper/scipy,jakevdp/scipy,lhilt/scipy,jakevdp/scipy,kleskjr/scipy,Gillu13/scipy,pschella/scipy,mdhaber/scipy,maniteja123/scipy,pizzathief/scipy,aeklant/scipy,josephcslater/scipy,pbrod/scipy,Eric89GXL/scipy,maniteja123/scipy,josephcslater/scipy,jor-/scipy,tylerjereddy/scipy,larsmans/scipy,anielsen001/scipy,perimosocordiae/scipy,Gillu13/scipy,surhudm/scipy,Gillu13/scipy,surhudm/scipy,haudren/scipy,niknow/scipy,argriffing/scipy,nmayorov/scipy,aarchiba/scipy,kleskjr/scipy,jamestwebber/scipy,Newman101/scipy,pyramania/scipy,argriffing/scipy,bkendzior/scipy,bkendzior/scipy,Gillu13/scipy,e-q/scipy,WarrenWeckesser/scipy,nonhermitian/scipy,anielsen001/scipy,anntzer/scipy,haudren/scipy,sriki18/scipy,aarchiba/scipy,zerothi/scipy,anntzer/scipy,niknow/scipy,matthewalbani/scipy,Newman101/scipy,behzadnouri/scipy,scipy/scipy,larsmans/scipy,bkendzior/scipy,gdooper/scipy,perimosocordiae/scipy,jakevdp/scipy,kalvdans/scipy,nonhermitian/scipy,rgommers/scipy,pyramania/scipy,josephcslater/scipy,haudren/scipy,niknow/scipy,larsmans/scipy,apbard/scipy,gdooper/scipy,maniteja123/scipy,Newman101/scipy,arokem/scipy,Eric89GXL/scipy,kalvdans/scipy,befelix/scipy,tylerjereddy/scipy,mikebenfield/scipy,Shaswat27/scipy,pbrod/scipy,zerothi/scipy,jor-/scipy,endolith/scipy,aeklant/scipy,arokem/scipy,perimosocordiae/scipy,e-q/scipy,jjhelmus/scipy,Eric89GXL/scipy,pbrod/scipy,anntzer/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,haudren/scipy,kleskjr/scipy,kalvdans/scipy,woodscn/scipy,mdhaber/scipy,aeklant/scipy,e-q/scipy,anielsen001/scipy,Eric89GXL/scipy,anntzer/scipy,maniteja123/scipy,larsmans/scipy,argriffing/scipy,ilayn/scipy,larsmans/scipy,grlee77/scipy,apbard/scipy,matthew-brett/scipy,scipy/scipy,gdooper/scipy,gertingold/scipy,mikebenfield/scipy