This introduces a new django_evolution.deprecation module, which

contains utility classes that warn about usage of deprecated

functionality. This includes the following stable classes:


BaseRemovedInDjangoEvolutionWarning: Base class for all deprecation

  warnings.


RemovedInNextDjangoEvolutionWarning: Indicates removal in the next

  major version of Django Evolution.


And version-specific classes, which are current as of Django Evolution

2.2 but will be added to and removed as needed:


RemovedInDjangoEvolution30Warning: Deprecation warning for features

  scheduled to be removed in Django Evolution 3.0.


RemovedInDjangoEvolution40Warning: Deprecation warning for features

  scheduled to be removed in Django Evolution 4.0.


RemovedInNextDjangoEvolutionWarning currently maps to

`RemovedInDjangoEvolution30Warning.
As of this change, there are no features flagged for deprecation, but

an upcoming change will begin to introduce deprecations.

Made use of this in an upcoming change.