Add some upgradeTo() restrictions:

. no empty upgrades
. at most one `auto()` migration
Suppress bunch of Robolectric warnings
Add error messages for onUpgrade restriction checks
Add basic schema tests and an error message
Fixed two tests failing on wrong check
Added one more test for invalid downgrade definitions
Add error messages for some invalid schema definitions
Simplify tests
Using consistent exception type for schema building issues
Better error messages for schema issues
More precise exception checking
Add test and error message for dropping non existing table
Add some logcat logs for ugprade process
Ensure correct offsets of upgradeTo/downgradeTo definitions
Workaround for cobertura plugin issues
Do not allow multiple upgrades for the same revision
Extract constant
Add basic tests for release markers
Move some stuff to test utilities
Better tests for fetching current revision number