Fiddle around with css_select_style()'s API. Add some documentation.
Fiddle around with css_select_style()'s API. Add some documentation.

svn path=/trunk/libcss/; revision=6285

prepare/netsurf_libcss,servo/libcss,zhuyadong/libcss,servo/libcss,prepare/netsurf_libcss,zhuyadong/libcss,zhuyadong/libcss,servo/libcss,prepare/netsurf_libcss