The Codec interface is now implemented by *pgtype.JSONCodec
and *pgtype.JSONBCodec instead of pgtype.JSONCodec and
pgtype.JSONBCodec, respectively. This is technically a breaking
change, but it is extremely unlikely that anyone is depending on this,
and if there is downstream breakage it is trivial to fix.
Fixes#2005.
Added ValueRoundTripTest to pgxtest
Removed pgtype/testutil
pgtype tests now run with all (applicable) query modes. This gives
better coverage than before and revealed several bugs which are also
fixed in this commit.