Add Postgres.js

[porsager]

Hi. Here's an initial shot at adding Postgres.js to the sql benchmarks. I've only implemented the 3 cases tested in the run for now.

By the way - awesome job on EdgeDB, I'm looking forward to have time to give it a closer look! I think it would be really cool to have a Postgres.js style surface api for the EdgeDB javascript (node/deno) driver

fixes #44