django_evolution.mutations was another big module with a lot of

complexity. To prepare for new logic that'll be coming soon, and new

mutations, this change splits up the module into some sub-modules and

sub-sub-modules.
All base classes and the Simulation class now live in

django_evolution.mutations.base.
All actual mutation classes live in their own respective sub-modules

within django_evolution.mutations.
These classes will continue to be imported via

django_evolution.mutations. There's no plan to deprecate this,

especially since this all evolution files have been generated to import

from here.
No code has been changed other than Version Added or Version Changed

docstring updates at module and class levels detailing the move.

All unit tests pass.