Feature Requests: Custom Tags, Filter by Elo, Extract Clock and Time data,

[DeFilippis]

I'm now using this library thanks to the MySQL database functionality. Having a hard time with extracting custom tags (e.g. BlackElo and WhiteElo).

LiChess also embeds clk and eval tags within moves (as seen in your readme file) which would be nice to put into a dataframe column. Also It'd would be nice to skip import of games where Black or White Elo doesn't exceed some value (e.g. 2200).