v0.12.6

• Handle a __models__ variable within modules to override the model discovery mechanism:
  If you define the __models__ variable in yourapp.models (or wherever you specify to load your models from),
  generate_schema() will use that list, rather than automatically finding all models for you.
• Split model consructor into from-Python and from-DB paths, leading to 15-25% speedup for large fetch operations.
• More efficient queryset manipulation, 5-30% speedup for small fetches.