Add syntax highlighting file for Go

Original nano commit: 4700
http://svn.savannah.gnu.org/viewvc?view=rev&root=nano&revision=4700
Original nano commit message:
 	2014-03-31 Chris Allegretta <chrisa@asty.org>
	      * doc/syntax/go.nanorc: basic go syntax highlighting
Merge branch 'master' into libtermkey