v0.0.9: Safer compilation and better error messages

Changelog

• compiler(#12): the compiler will now let you know when you're
  redefining a function on the OCaml side, which is not allowed on the
  Erlang side and stop compilation.

• compiler(#16): shadowing bindings with let are (for) now unsupported
  on the OCaml side, which makes translation runtime safe. We won't see
  any more X = X + 1 on the Erlang side.

• compiler(#15): to help with #16, priming of variables is now supported
  and translated to valid Erlang. We can write x' = x + 1 and it will
  translate to X_prime = X + 1.

• compiler(#13): recursive let bindings within a function definition are
  now not supported since they don't have a direct Erlang equivalent and
  require runtime overhead.

• error messages have been created for all of the above