We still cannot include elixirscript from github into a project. Running mix deps.get && mix compile does not build the initial Core.js. We need to clone elixirscript, make, then use elixirscript via path in our mix.exs.

I am proposing to integrate 2 features here when doing mix compile.

1. if Core.js is missing, if yarn is missing, give error Yarn not found, install it here http://.....
2. if Core.js is missing, if yarn is present, run make