Release 0.2.0

Lots of breaking changes, not sure I list them all here

• Serde support with the serde feature
• Rating and friends renamed to PublicRating and similar
• InternalRating and friends renamed to ScaledRating and similar
• No more super weird generic stuff in algorithm
• Support for mostly accurate instant Glicko-2 ratings without bookkeeping, see algorithm::rate_game(s)
• Algorithm was completely changed up in general with new and changed types, check docs for that

Less breaking changes

• Protection against infinite loops (see constants::MAX_ITERATIONS)
• Probably some other stuff too

No migration guide and maybe there's stuff I missed, sorry, it's in version 0.X so that's my excuse.