PGN parser - help needed!

[ornicar]

We need a dart PGN parser for the next lichess mobile app.

A good first version would parse a linear sequence of moves, no variations, no comments.

It's recommended to mimic the chessops typescript library:

• tests
• implementation

This is a good first issue to get started with the dart language, and therefore with the development of the next mobile app.

Please drop by our discord server to discuss it https://discord.gg/lichess

EDIT:
One request: we should strive to have an immutable API because the rest of dartchess is immutable. Internal implementation can be mutable of course, for performance considerations, but the resulting Game type should be immutable.