Support repeatable migrations

[jeremymailen]

It's very useful to have migrations that can be re-run whenever the migration file changes. For example if you have views or stored procedures to maintain over time. Example of how Flyway supports them.

[igorvoltaic]

Liquibase has this too, but with an option "run-always:true" to run only needed files.

In dbmate I normally just change the version in filename to run the same file.

[jeremymailen]

Oh, this is a good idea. I guess dbmate doesn't validate the presence of all prior migrations so you could put views in one migration file and bump the timestamp when they change, effectively making them repeatable.