Compatibility with the Django password validators API

[acdha]

I recently found a bit of code which had been copied with only slight modifications to use ComplexityValidator in AUTH_PASSWORD_VALIDATORS. Would it be worth tossing together a pull request which adds a compatibility shim for that, similar to the code below?

https://github.com/LibraryOfCongress/concordia/blob/2b8605e388323770fde79975b140bb7c4776c6cb/concordia/validators.py

[maccesch]

Yes that seems like a good idea! Would you mind creating a PR for this?

[acdha]

@maccesch I started this in #54 but it doesn't have the other validators yet because I was debating some of the naming options first.