Add the go ctags parser

Make go one of the builtin filetypes, add the parser and update the related
source and config files. While there, remove Rust from [Groups] in
filetype_extensions.conf because it's already a builtin filetype as well.

The parser itself is stolen from the fishman/ctags repo.

The parser is more on the simple side - types like structs or interfaces are not distinguished (I may have a look at it in the future if I have time, should be easy to add) but it's definitely useful for going to tag definition/declaration.

I hope I have changed all that should have been changed and haven't forgotten about anything. Everything seems to work just fine, including syntax highlighting, build commands sidebar symbols, goto tag definition/declaration.
On Fri, Nov 7, 2014 at 7:04 PM, Colomban Wendling <notifications@github.com>
wrote:

> In src/highlightingmappings.h:
>
> > @@ -624,6 +624,17 @@ static const HLKeyword highlighting_keywords_FORTH[] =
> >  #define highlighting_properties_FORTRAN		highlighting_properties_F77
> >
> >
> > +/* Go */
> > +#define highlighting_lexer_GO		SCLEX_CPP
> > +#define highlighting_styles_GO		highlighting_styles_C
> > +static const HLKeyword highlighting_keywords_GO[] =
> > +{
> > +	{ 0, "primary",		FALSE },
> > +	{ 1, "secondary",	FALSE }
> > +};
>
> why not mapping it to highlighting_keywords_C? Also it misses docComment
> that is used in the filetype file
>

Frankly I didn't know very well what I was doing in this file - my
assumption was this was pointing to the filetypes.go file and the keywords
defined there but if something else is needed please fix it. And yes, I
forgot the docComment.