PR: Implement support for "CTL" processor.

[KelSolaar]

Summary

This PR implements support for a CTL processor as described in #975.

Preflight

Code Style and Quality

• Unit tests have been implemented and passed.
• Mypy static checking has been run and passed.
• Pre-commit hooks have been run and passed.
• [NA] New transformations have been added to the Automatic Colour Conversion Graph.
• New transformations have been exported to the relevant namespaces, e.g. colour, colour.models.

Documentation

• New features are documented along with examples if relevant.
• The documentation is Sphinx and numpydoc compliant.

[KelSolaar]

@aforsythe and @scottdyer for VIS!

[coveralls]

Coverage decreased (-0.2%) to 99.658% when pulling 25672a7 on feature/ctl_processor into bcdf228 on develop.

[KelSolaar]

I will merge this one!