Expose more game metadata

[Shadow53]

There is metadata available on a game's webpage under "More Information" that is not available through butler. The specific metadata I'm looking at are genre and tags, though there may be more that I'm not aware exists as a consumer.

Use case: programmatic sorting of downloaded files into folders by specific tags, especially for assets and books; automatic application of tags to books e.g. for Calibre import.

[Shadow53]

Being able to filter searches by this metadata would also be useful, though for my needs it would suffice to just include it in the Game struct.