Evaluate Pg 13 support

[pgguru]

As discovered in work for #57 there are some additional things needed to get Pg 13 support in full or part.

#57 (comment)

See about supporting or disabling the 2 things that are failing with 13 support, mainly:

• COPY FROM ... WHERE handling —seems this uses a different mechanism in 13
• including row or array types of user types.

On the second point, array_recv in 13 seems to not support this and blows up, so the question is between 1) use text support instead of binary for these types, or 2) throw an error in 13 if we encounter these. I'm leaning towards option 2 here since the utility of having this module work with binary copy seems higher to me than custom composite types which are largely a minority of data that might be handled by this module (particularly when you're looking at the lower end of the supported spectrum.)