Be clearer about "parsing" vs "serialization" terminology

[henrikhorluck]

From https://www.merriam-webster.com:
Parse:

to divide (a sentence) into grammatical parts and identify the parts and their relations to each other

Serialize (and deserialize):

Serialize: to arrange or publish in serial form

This makes the naming of RosMessageParser.MessageDataParser particularly confusing, as it actually (de)serialises a message. Note that with #56, it is likely that all serialization will be part of each generated class, so this whole class should probably be removed?