First stable release

• Add configuration file migration-snapshot.php
• Implicitly dump after migrate:rollback
• Reorder migrations rows within dumps to avoid noise in source control as migrations are developed in parallel
• Trim leading underscores from names of foreign key constraints with Mysql to workaround pt-online-schema-change quirk
• Append new line to the end of all dumps, not only Sqlite, for simpler diffs in source control