[Tokio-Postgres] Error handling: Make tokio_postgres::error::Kind public #790

[BaptisteRoseau]

Feature request for #790

Make tokio_postgres::error::Kind public to enable users to match on it from a tokio_postgres::error::Error.

@sfackler I made two commit: one that returns a reference, the other that returns a cloned tokio_postgres::error::Kind instance. I was not sure whether it was not clonable on purpose or not.

Please see this comment for more details: #790 (comment)

[BaptisteRoseau]

@sfackler any chance to merge this PR ?

It's been requested here #790 and has been waiting for a while.
Documentation and test case were added too, what would be missing to merge ?