Support elixir-ts-mode

[tjtrabue]

Hey @mickeynp, first of all, this is an amazing Emacs plugin! I cannot tell you how much better you have made my Typescript editing experience since releasing Combobulate. It's easily one of my favorite new Emacs plugins. Now that Elixir has tree-sitter support, I was wondering if we could get Combobulate support for Elixir files? I program in Elixir all the time, and having syntactically-aware editing commands available would be a game-changer.

Thank you so much! -tjtrabue