Update Checker - add support for annotated types

[ktec]

[d2km]

Looks good to me.

If you could add a unit test here https://github.com/d2km/rtypes/blob/master/test/rtypes_test.exs that would be awesome.

I'm thinking something along the lines https://github.com/elixir-lang/elixir/blob/82dca5537a4956b33367cf05d694894055c7ce80/lib/elixir/test/elixir/typespec_test.exs#L548