added gedit 3.0 solution.

For gtksourceview 3.0 (gedit 3.0), user: 
    mkdir -p ~/.local/share/gtksourceview-3.0/language-specs/ && wget https://raw.github.com/LearnBoost/stylus/master/editors/gedit/styl.lang -O ~/.local/share/gtksourceview-3.0/language-specs/styl.lang