Integrate goto functionality with tags

_From @lencioni on January 31, 2016 18:40_

This is a bit of an unfinished thought, but the goto functionality feels very similar to tags. (See `:help tags`) It occurred to me that perhaps we could integrate with tags somehow, but I'm not sure exactly what that would look like just yet. Some ideas come to mind:
- Maybe there is a way to hook into the tags resolver built into vim. If this is possible, we should be able to call the goto feature at this time.
- Perhaps a command could be added to parse a project and generate a tags file. This could be appended to the tags file generated by a tool like exuberant ctags. This fees pretty messy though, since the format of that file depends partly on the tool that created it and partly on the configuration given to that tool.
- [Exuberant ctags is able to be extended with new parsers](http://ctags.sourceforge.net/EXTENDING.html). Perhaps we could figure out a way to integrate import-js in that way, but it seems a bit out of scope.

This is pretty low priority, so I'm adding the help wanted tag.

_Copied from original issue: Galooshi/import-js#179_

The issue names no files, tests, or implementation entry points. Start with Vim's `:help tags` and the cited Exuberant ctags extension documentation, then determine whether a tags-resolver hook or tags-file generation is feasible; done requires a defined integration approach, which the issue does not yet specify.

Written by the indexing model from the issue text.