Add compatibility with Lichess PGNs (support for multiple games, support for move nits)

[vladkvit]

The code now supports parsing multiple games and moves such as " 2. f4?! { [%eval -0.26] } "

Known issues:

The move parsing code will still (just like in the upstream repo) inconsistently parse lines like this:

1. e4 { [%eval 0.25] } 1... e5 { [%eval 0.3] } 2. f4?! { [%eval -0.26] } 2... exf4 { [%eval -0.24] } 3. Nf3 { [%eval -0.29] } 3... Be7 { [%eval -0.24] } 

The issue is that the move number is repeated twice and thus the moves aren't grouped together like they should be.

The performance of this code is still slower than python-chess's PGN parse.