Methods defined on T are also available on *T. This change makes Value
consistent with database/sql Value implementations. It also makes Value,
EncodeBinary, and EncodeText more convenient to use because you can
pass T or *T as an argument to a query.
The MarshalJSON change is even more significant because without it
json.Marshal would generate the "%v" format instead of the implemented
MarshalJSON.
Thought this technically changes the interface, because *T will be
automatically dereferenced as needed it shouldn't be a breaking change.
See: https://github.com/jackc/pgx/issues/538 for initial discussion.
