gix-config towards 2.0

[Byron]

Towards 2.0

• full serde serialization support (maybe) - the current one is only partial.
• resolved config (optimized for reading, no round-tripping) is created directly from parse events (like git does)
• 100% correct date parsing with gix-date
  • This includes parsing expiry dates, probably as its own top-level type in comfort.rs.

Other Ramblings

• Could gix-config use self-referential structures like in ignore to avoid copying everything into Cow<'static, [u8]> effectively.
• tracking issue of 1.0 release