DJI Gimbal Metadata

This version searches both:
  - the first 4 MB of each supported file, and
  - if needed, the last 4 MB.

This accommodates DJI DNG files where the gimbal XMP metadata is stored
near the end of the file.

Only DNG, JPG, and JPEG files are examined. Other selected file types are
reported as:
  Skipped - Not DNG/JPG/JPEG

Yaw, Pitch, and Roll must all be found before metadata is written.
Original image files are not modified.
