* regular SHA256 is not secure
* added code to auto migrate old passwords to the new password_hash if the existing password_hash matches either of the old password generation schemes.
- Added type hinting (for now, 3.5-compatible)
- Split `db` namespace into `db` module and `model` namespace
- Changed elastic search to be created lazily for each operation
- Changed to class based approach in entity serialization to allow
stronger typing
- Removed `required` argument from `context.get_*` family of functions;
now it's implied if `default` argument is omitted
- Changed `unalias_dict` implementation to use less magic inputs
