We're holding back two things:
- Postgres 12 and up breaks `libpq-sys`.
- Ubuntu 20.04 breaks `sqlx`.
We intend to merge this branch as the main release.
Fixes#27, or at least works around it.
This deals with the issues mentioned in
https://github.com/sgrif/pq-sys/pull/18, and it relies heavily on ideas
from @golddranks and @clux.