Merge two revisions together.  Creates a new migration file

def merge(directory=None, revisions='', message=None, branch_label=None,
          rev_id=None):
    """Merge two revisions together.  Creates a new migration file"""
    if alembic_version >= (0, 7, 0):
        config = current_app.extensions['migrate'].migrate.get_config(
            directory)
        command.merge(config, revisions, message=message,
                      branch_label=branch_label, rev_id=rev_id)
    else:
        raise RuntimeError('Alembic 0.7.0 or greater is required')