postgres-uno support

[mlybarger]

our team has a LOT of microservices built with nodejs using postgres-uno to connect to and communicate with a postgres database (RDS). we're looking to use pg-mem for unit testing, but I don't see how to inject the pg_mem instance/connection into our postgres-uno.

https://github.com/wildbillh/postgres-uno/blob/master/lib/postgres-uno.js