Provide a faster way of generating PGN files.

[RogerMarsh]

PGN files need to be generated as input for the CQL program which evaluates queries.

The initial attempt to do this in a faster way failed and was removed at f988d1d.

[RogerMarsh]

Faster generation of PGN files may be possible if movetext like 'Qb1c2', sometimes necessary to identify which queen is moving to c2, could be held on the database as 'Q1bc2'. The text 'Q1b' is not valid movetext in a PGN file.

[RogerMarsh]

Allowing 'Q1bc2' in pgn-read seems difficult to control. RogerMarsh/pgn-read@8d53bd0 provides a method which decides if fully disambiguated moves could be present in the PGN for a game. The monthly LiChess download for January 2017 contains 10 million games of which a few hundred have fully disambiguated moves. 6745b2e uses the method to decide which PGN parser is appropriate and cuts the time to generate the 10 million game PGN file from over 6 hours to 1 hour.