SQLite backend doesn't require PostgreSQL driver.

Fix closure support for `getDb` proc parameter of `newPool`

Add `select` and `selectAll` flavors that work on types instead of

object instances.

- [f] Fix connection pooling for Nim 2.2.0.

- [d] Update code docs for the improved docgen in Nim 2.2.0.

Make creating indices idempotent.

Add the ability to set custom schema for PostgreSQL.

Update db_connector required version.

- Enum support.

- x1000 performance boost on bulk updates.

Add compatibility with Nim 2.0.

This release is a result of hard work by @PhilippMDoerner. Huge thank
you to him!

Also, huge thank you to @ringabout for their assistance with the PR
review.

You guys rock!

1. Optimized select for a single record.

2. Improved SQLite foreign key policy.

New admin joined the repo. It's super effective! Show your love to
@PhilippMDoerner!