Add ppp_datamodel/communication.py.
Fix previous commit.
Test new code.
Improve tests coverage.
Add .as_json() to Request and Response.
Add as_dict().
Fix typo and make tests not dependant on serialization order.
Fix typo leading to misinterpretation of the doc in the implementation.
Allow both tree and sentence in a request.
Add full support for sentences.
Fix repr.
Make __eq__ strict on types.
Merge pull request #8 from ProjetPP/add-communication

Add ppp_datamodel/communication.py.