Put your migrations in this folder.

Rules:
- a migration file must have the extention .sql or .SQL
- name the file with a number at the beginnig to controle the order you whant your migrations
to be applied with DB.migrate_all().

Beware:
If you modify a migration file after it have been applied, silly_db will
consider it as a new migration (even if the name remains the same),
it will then be applied again.
