Migrations
If you take a look at the Database class, there are some undocumented methods that may be of help:

https://github.com/coleifer/peewee/blob/master/peewee.py#L456

Say you're renaming a field... from 'foo' to 'bar':

`database.execute(database.rename_column_sql(FooModel, 'foo', 'bar'))`

I'll see about getting this into the docs.

Just curious if you have thought about migrations in peewee. If not an automated way, is there an idiomatic way to do it with peewee besides changing fields and guessing the needed SQL statements to reflect them?
