added support for background-clip
added support for background-clip

ilovezy/nib,ecmartinez/nib,ecmartinez/nib,rstacruz/nib,JulianWielga/stylus-less,ilovezy/nib,F4-Group/nib,seleckis/nib-pushup,F4-Group/nib,tj/nib,tj/nib,seleckis/nib-pushup