Internal Refactors

The internal modules for the compiler and the typing experiments are
split now, and the Erlang support is unified in a single library that
only depends on the standard library and the Sexplib library for
deriving Sexp representations.

The goals here are:

• make the codebase easier to hack on in general -- there's still work
  to do here, as I think the ideal structure would be flatter than it is
  right now.

• prepare the Erlang library for continued work -- extending the lexer
  with positioning information on every read token will help parametrize
  the AST with contextual information. This would aid in error
  reporting.

• establish clearer compilation and type checking paths:

  • from OCaml to Erlang,
  • from OCaml Lambda to Core Erlang,
  • from Erlang to Native binaries.