Create compiler manifest

[bryanjos]

The manifest should capture the information about the modules compiled and the output for that module. Ideally, it would have the following information.

• Module name
• Beam file path
• Beam file timestamp
• JS file path
• JS file timestamp

It should also capture the compiler version.

Mix.Project.manifest_path will show the path to where manifest files are expected to be. Elixir saves it's manifest files as .compile.elixir so ElixirScript should save its own as .compiler.elixir_script

[bryanjos]

I'm not sure at what point in the compilation process this file should be created

[bryanjos]

Some examples of how Elixir creates and uses manifest files:
https://github.com/elixir-lang/elixir/blob/540c973d921009e7e129d7279b03ec8bb92449f2/lib/mix/lib/mix/compilers/elixir.ex