doc: extracted mod docs, added example in uix/behaviors/button.py
doc: extracted mod docs, added example in uix/behaviors/button.py

janssen/kivy,aron-bordin/kivy,Cheaterman/kivy,tony/kivy,CuriousLearner/kivy,andnovar/kivy,LogicalDash/kivy,rnixx/kivy,rafalo1333/kivy,rafalo1333/kivy,Cheaterman/kivy,LogicalDash/kivy,jkankiewicz/kivy,vitorio/kivy,manthansharma/kivy,akshayaurora/kivy,kived/kivy,Cheaterman/kivy,jegger/kivy,inclement/kivy,LogicalDash/kivy,kivy/kivy,rnixx/kivy,KeyWeeUsr/kivy,KeyWeeUsr/kivy,andnovar/kivy,arlowhite/kivy,bionoid/kivy,darkopevec/kivy,bionoid/kivy,darkopevec/kivy,kivy/kivy,manthansharma/kivy,KeyWeeUsr/kivy,Cheaterman/kivy,jegger/kivy,darkopevec/kivy,jkankiewicz/kivy,akshayaurora/kivy,autosportlabs/kivy,el-ethan/kivy,inclement/kivy,aron-bordin/kivy,tony/kivy,matham/kivy,darkopevec/kivy,rnixx/kivy,bionoid/kivy,CuriousLearner/kivy,autosportlabs/kivy,manthansharma/kivy,LogicalDash/kivy,matham/kivy,autosportlabs/kivy,andnovar/kivy,matham/kivy,arlowhite/kivy,vitorio/kivy,el-ethan/kivy,el-ethan/kivy,kivy/kivy,cbenhagen/kivy,manthansharma/kivy,janssen/kivy,akshayaurora/kivy,tony/kivy,inclement/kivy,jegger/kivy,arlowhite/kivy,cbenhagen/kivy,jegger/kivy,aron-bordin/kivy,jkankiewicz/kivy,rafalo1333/kivy,aron-bordin/kivy,KeyWeeUsr/kivy,cbenhagen/kivy,jkankiewicz/kivy,bionoid/kivy,kived/kivy,kived/kivy,janssen/kivy,matham/kivy,CuriousLearner/kivy,janssen/kivy,vitorio/kivy