Migration directory

[slightlytyler]

Instead of having migrations clogging up the root would be great to have them in migrations/ as a default and allow for a CLI option to set the directory

[charlieschwabacher]

I like it 👍 - I'm thinking it makes sense to create it the first time they choose to write a migration to a file (and not as part of the initial scaffold), just to keep the initial project uncluttered / easy to understand. If you want to do another pull, I'll merge it.

[slightlytyler]

I might be able to put something together this weekend