Updated doc of AliasProperty.
Updated doc of AliasProperty.

kivy/kivy,matham/kivy,inclement/kivy,matham/kivy,rnixx/kivy,inclement/kivy,inclement/kivy,kivy/kivy,rnixx/kivy,rnixx/kivy,kivy/kivy,matham/kivy,akshayaurora/kivy,akshayaurora/kivy,matham/kivy,akshayaurora/kivy