Emmett 2.4 Edison

This was huge. With almost 7k lines diff from previous release, 2.4 is focused on Python 3.10 support and ORM features.
Due to the already consistent amount of changes, some features originally planned for this release were postponed to next major release.

Thanks to all the community for their patience, with a special mention to @Kkeller83 who keeps sponsoring Emmett project and @treelym who sponsored the project for a couple of months since last major release.

Changes since 2.3:

• Added official Python 3.10 support
• Added relative path support in templates
• Added support for spatial columns in ORM
• Added support for custom/multiple primary keys in ORM
• Added support for custom/multiple foreign keys in ORM
• Added support for custom and multiple primary keys relations in ORM
• Added watch parameter to ORM's compute decorator
• Added save method to ORM's rows and relevant callbacks
• Added destroy method to ORM's rows and relevant callbacks
• Added refresh method to ORM's rows
• Added before_commit and after_commit ORM callbacks
• Added changes tracking to ORM's rows
• Added support to call super rowmethod decorated methods in ORM models
• Added migrations set command to CLI
• Added skip_callbacks parameter to relevant methods in ORM
• ORM now automatically adds appropriate indexes for unique fields

As usual, upgrade guide is available in the docs