Type mappings

[s2hc-johan]

To allow for better interaction between erlang and python we should modify and or allow for user to change the mapping between types.

For the most part I think that this would be more sane and closer to what people would expect
erlang string (list of integers below 255) -> py list
erlang list -> py list
erlang binary -> py binary

py list -> erl list
py str -> erl binary (with default utf-8 encoding)
py binary -> erl binary

This could potentially solve the issues in #2