Migrate to default branch main.
## Craft new releases
-1. Get next _version code_ (master branch): `git rev-list HEAD --count master`
+1. Get next _version code_ (master main): `git rev-list HEAD --count main`
2. Decide on _version name_ (semantic versioning)
3. Manually update _version code_ and _version name_ in `build.gradle`
4. Create changelog (`_version code_.txt`)
