[feature request] add ability to pass options to gtags command (to filter/exclude files)

[dsummersl]

For larger projects gtags generates ginormous files including 3rd party dependencies I don't care about - it would be great if it were possible to, at a minimum, generate the files that gtags processes. Ideally having the ability to respect ignored things in a SCM .ignore (.hgignore, .gitignore, etc) would be even better.

[jsfaint]

I don't have much time on this.
PR will be appreciated 😄

GNU Global don't have built-in ignore support.
But it supports file list, maybe we can generate a file list and then remove the ignore file from it