Fork with pgx/v4 support and couple more improvements

[vgarvardt]

Hi.

Thank you for the library! I'm using it for couple my pet projects and wanted to improve it a bit and add some missing features. My PRs did not get any attention so I decided to clone the project and work on it - you can find it here https://github.com/vgarvardt/gue/tree/v1. My project references original one (this) and has the same license - MIT. Some APIs changed, but internally it is fully backward compatible with this one - table name and structire, all the queries are the same.

Some of the key changes are:

• both pgx/v3 and pgx/v4 support via db adaptor
• no more prepare statement call required on new connection being established in the pool
• logger adapter with couple implementations bundled