Realm 10+

Bump to v2.1.0 (#2)

* Bump to v2.1.0

- Upgraded Realm to 10.0+
- Upgraded BackgroundRealm to 3.0+
- Upgraded min iOS to 12+, tvOS to 12+ and macOS to 10.12+

* Changed to main branch

The big release

BLResultsController is here!