remodel v0.2.0

This release features the introduction of ObjectHandler which, from now on, is responsible for table-level operations made on the model (such as create, get or filter). Therefore, a Model will solely handle row-level operations (like save or delete). Even more, ObjectHandler represents the base for operations made on a model's one-to-many and many-to-many relations -- this means it is possible to do things like user['posts'].filter(accepted=True) or recipe['ingredients'].count()!

New features:

• introduction of ObjectHandler;
• several table-level operations: get, create, get_or_create now available for related models, and count for both models and related models.

Improvements:

• revamp of ObjectSet: len, __getitem__ are now available, plus lazy evaluation;
• switched to inflection module for handling table names;
• moved testing to tox;
• squashed various bugs.