Add Eq, ParialEq and Hash to ConnectParams (etc)

[amandasaurus]

I wanted to be able to use ConnectParams as a key of a hash (to do simple connection pooling), so I've added these Derives.

[sfackler]

Thanks!

[amandasaurus]

Could you please bump the version of postgres-shared and the dependency in postgres's Cargo.toml. Current version of postgres-shared is 0.4.0 which predates this patch being accepted

[sfackler]

Done!