Semantic versioning for migrations

[calebmer]

Instead of naming my migration files like so: 001_hello.up.sql. I would much rather use semantic versioning to name my migrations, e.g. 1.0.0.up.sql. All the files are still in the correct alphabetical order, but migrate won't recognize these files.

[mattes]

I think we are moving towards timestamps for versioning. See #58