Add copyright, project and license to top of header/implementation
Improve behaviors around opening/closing databases
Switch to 1 transaction per migration. Add userInfo, errors, and tests for cancellation during migration.
Guard against being initialized with unexpectedly nil values
Improve behaviors when the migrations table is not yet present

This change avoids unnecessary query errors by examining the database state ahead of querying.
Fix breakage under iOS
Add changelog
Bump version to 1.2.0