[Catalog]/[Tutorial]: Centipede game #804

One of the earliest mentions of Gambit is in the McKelvey-Palfrey experimental paper on the centipede game:

McKelvey, Richard D. and Palfrey, Thomas R. (1992) An experimental study of the centipede game. Econometrica 60(4): 803-836.

A few of the game models from the paper are currently in contrib/games (as cent*.efg).

We should:

1. Move the games into the catalog, improving their descriptions and cross-referencing them as appropriate
2. Create a tutorial illustrating the calculations from the original paper.

An amusing side note is that the original paper acknowledges the use of a CRAY XMP for calculations. We expect the calculations can largely be reproduced now in a Jupyter notebook!