Add "Special Thanks To" Section to documentation and About window

[david-cattermole]

Feature

Some users would like a "special thanks to" section in mmSolver to list people that haves significantly contributed feature ideas and/or provided feedback and helping the development of mmSolver.

The suggestion is to add the names to:

• The About window in the mmSolver Solver UI.
• The AUTHORS.txt file.

I will also add a link to the AUTHORS.txt file on the documentation page.

[david-cattermole]

This is added now.

More names may be added in future.