update workflow to include tags

• fix typos
• be consistent in using comments/tabs
• update README
  thanks to Uwe Hermann for the diff

add Dockerfile and Workflow

• include string.h
• linting

Install Ben's patch.

• commented the code a little so curious people can more
  easily learn a little about stereograms
• improved the default character-set
• improved randomization of line offsets to avoid 2 lines
  starting near the same spot
• added a randomizing seed command line argument
• fixed bug in the output: at borders between 2 different
  depths, sometimes a character that was supposed to be at the depth
  of the background looks like it's at the depth of the foreground.
  This was fixed by detecting when this happens, and replacing the
  character with a random character. This doesn't cause any visual problem,
  because these characters on the bottom side of such a depth border would
  only be seen by one eye in the real world, so it doesn't need to match up
  with any other character.

AA3d initial checkin - version 1.0