Complete R2T2 playgrounds, with authors, descriptions, and links.

This PR adds the complete R2T2 playground, in its initial and final configurations, including two E-pucks to simulate restarting the generator.

Authors, descriptions, and links are added to the r2t2 and the maze-6x6 playgrounds.

Since the description of maze-6x6 is in the playground, does it need to be in a separate file?