Only delete EMPTY paired pipes

Also indent with tabs, in keeping with the originals.
Add highlighting for Ruby 2's %I syntax

This is mostly derived from MattDMo's excellent work, as pointed to
from: http://www.sublimetext.com/forum/viewtopic.php?f=3&t=14387

I added support for %I, and removed %R; the latter does not appear to
be supported by Ruby 2.1, and I can't find documentation for it
anywhere.