Add ctags entries for Elixir

[mauricerkelly]

I'm opening this PR to invite some discussion on the addition of Elixir support in this package.

As an initial source, I took the Elixir support from the ctags file in the symbols-view package and have performed some edits to make it match more closely with what I was already seeing in the ctags file. As I delve further into the options available with ctags I'll update this PR. Happy to take feedback as well.

[nicolashainaux]

Hello,

I did add something similar, some time ago, in my forked package symbols-tree-nav. This is in the master branch, in one of the last commits, though I haven't published it yet. I don't know Elixir and have basically added the lines from symbols-view's ctags too, as far as I remember. It would be nice if you could open the same PR in symbols-tree-nav, so this enhancement could be included in its next release.

If in the future you have such enhancements to propose (as PR or issues), you are welcome to add them to symbols-tree-nav too!

[mauricerkelly]

I've taken some time to review this further and I think it seems to work okay with the Elixir sources I have been working with.