Umbrella apps support

[nurges]

Elchemy gives an error when executing 'mix compile' in an umbrella app.

It is caused by a format command in elchemy/lib/mix/tasks/compile.elchemy.ex

Mix.Task.run("format", ["lib/**/*.elchemy.{ex,exs}"])

A workaround is to create a 'lib' folder in umbrella app root and copy 'Hello.elchemy.ex' into this folder.

[wende]

@nurges Great find!
I think given that we just want to format all of the elchemy files it could be changed to just "./**/*.elchemy.{ex,exs}" assuming such a wildcard works correctly

[wende]

After investigating an issue it seems that to make it work for umbrella apps it'd require a lot of changes to the main bash file, which is undergoing a big overhaul anyway due to #288.

Elchemy can still be used in every single app inside of the umbrella app. That means that the code between the apps can be used on an elixir interop (with ffi or using Elixir injection) but not on an Elchemy interop (It won't see the types out of the app)

Putting this to the backlog after dependency gets of #288 gets fixed