Fix up doc formatting, use spaces for alignment (tabs are for indentation only).
Fix up doc formatting, use spaces for alignment (tabs are for indentation only).

This fixes issue where if user has tab width other than 4, some lines will become misaligned. For example, see the package description at https://godoc.org/github.com/gorilla/mux.
kiip/mux,jboelter/mux,buddhamagnet/mux,gorilla/mux,studygolang/mux,Vorstack/mux,coolljt0725/mux,wfxiang08/mux,TramPamPam/mux,heetch/mux,pH14/mux,matk86/mux,w4ngyi/mux,dvln/mux,Manbeardo/mux,Arkan/mux,laohanlinux/mux,Gorilla/mux,muroachanf/mux,scriptoLLC/mux,outrightmental/go-mux,vonwenm/mux,gopherlabs/gopher-providers-mux,CedarLogic/mux