Fixes#93 - Add 'changes_display_dict' property to 'LogEntry' model to display diff in a more human readable format
'changes_display_dict' currently handles fields with choices, long textfields and charfields, datefields, timefields, and datetimefields. Supports `django-multiselectfield` with choices and Postgres's ArrayField with choices.
Textfields and Charfields longer than 140 characters are truncated with an ellipsis appended.
Date, Time and DateTime fields are rendered according to `L10N`, or if turned off fall back on Django settings defaults for DATE_FORMAT, TIME_FORMAT and DATETIME_FORMAT.
A new kwarg was added to 'AuditlogModelRegistry' called 'mapping_fields'. The kwarg allows the user to map the fields in the model to a more human readable or intuitive name. If a field isn't mapped it will default to the `verbose_name` as defined on the model or the Django default `verbose_name`. Partial mapping is supported, all fields do not need to be mapped to use the feature.
* Add django-multiselectfield test dep
* Add psycopg2 test dep
* Add postgres testing database and router
* Add postgres support to travis builds
* Add support for multiple databases. LogEntry saves to same database of the model its associated to
* If any literal evals fail default to None
* Add support for Postgres ArrayField in changes_display_dict
* Revert to old travis image while they are fixing issues with it
* Update docs
* Add full test coverage
