In an effort to better namespace Django Evolution settings and keep them

manageable, this change introduces a new settings.DJANGO_EVOLUTION

dictionary. Currently, this supports CUSTOM_EVOLUTIONS and ENABLED

keys, but will later include a CUSTOM_MIGRATIONS setting.
The old settings.DJANGO_EVOLUTION_ENABLED and settings.CUSTOM_EVOLUTIONS

are still supported, but will emit a deprecation warning.
All settings are now accessed through a new

django_evolution.conf.django_evolution_settings object, which is an

instance of DjangoEvolutionSettings. This manages loading settings (both

modern and legacy), defaults, and responding to Django's settings_changed

signal.

Unit tests pass on all versions of Django and Python.
Manually tested the values by tweaking Django settings and running management

commands.