Adds support for CockroachDB. Cockroach uses the postges wire
protocol and has a large amount of common SQL functionality shared
with Postgres, so much of the postgres code was able to be copied
and modified.
Since the protocol is used in determining the driver, and the
Postgres protocol is also used by Cockroach, new connect string
prefixes were added: cockroach:// cockroachdb:// and
crdb-postgres://. These fake protocol strings are replaced in
the connect function with the correct `postgres://` protocol.
TODO: Tests needed (Cockroach has a docker image, so this shouldn't
be too hard)
Dale Hui
Taylor Wrobel