Add tag generation for the module code

Adds ctags support for chapel via a new utility script, `chpltags`. `chpltags`
uses the regex options supplied by ctags and etags.

`ctags -e` is now used to generate the emacs format for compatibility
with these options if possible, otherwise etags is used.

Also consolidated a few rules in the .gitignore for tag files, we now
generally ignore any tags or TAGS file.
Could be simplified to: `return out and ('Exuberant Ctags' in out) and ('+regex' in out)`.