lensfun: Credits

# Credits

So far this is a solo project, so the only code contributor for now is:

- Andrew Zabolotny <zap@homelink.ru>

The following people directly or indirectly contributed to the birth and growth of this library:

- Thomas Niemann for the original open-source PTLens software and database.
- Pablo d'Angelo for the idea of a open-source lens database.
- The whole PanoTools team: for all math and knowledge I have borrowed from PanoTools.
  - Helmut Dersch - The father of most (all?) open-source panorama creation tools.
  - Daniel M. German
  - Kevin Kratzke
  - Rik Littlefield
  - Fulvio Senore
  - Jim Watters
  - Thomas Rauscher
  - Pablo d'Angelo (thanks once more :)
  - Bret McKee
  - Robert Platt