Make set/get_encoded_data into a real property.

This changes the semantics such that accessing the 'data' property
will cause the encoded data to be deserialized. The converse is also
true: accessing the 'encoded_data' property causes the Python data
types to be serialized. If a proper encoder or decoder is not
registered for the object's content-type, an exception will be raised.
This means that the assumption about 'data' as a string being
equivalent to 'encoded_data' is no longer valid and existing code that
relies on that assumption will break.
Use TypeError instead of RiakError.
RiakObject._encode_data is no longer used.
Deprecate new_binary and new_binary_from_file.
Merge pull request #213 from basho/sdc-remove-binary

Make set/get_encoded_data into a real property.