Revert to previous version of PGN parser

The regular expression PGN parser would fail in certain situations
(eg. moving pinned pieces when move disambiguators where not needed -
search tests.js for 'broken PGN parser' for specific instance).

This fix compares all incoming moves in load_pgn() to chess.js generated
SAN.  This method is slower, but accurate.  All move decorations
(eg. Nb4+?!) are stripped from the PGN moves to allow for looser
parsing.

Fixes #55.