Feature Request: Transaction configuration on a per migration basis

I'm submitting a...

• Bug report
• Feature request
• Question

Current behavior

There is no way to turn off transactions for individual migrations.

Expected behavior

Certain migrations need to be run outside of a transaction. For example, in PostgreSQL, ALTER TYPE type_name ADD new_value cannot be run in a transaction. The rest of the migrations, however should be run in a transaction. There is currently no way to configure individual migrations to not use a transaction block. It would be extremely helpful to allow this to be part of the configuration for a single migration.