v0.2.0+commit.b20af5f

fix: all `pgmigrate ops` commands were failing (#13)

Fixes https://github.com/peterldowns/pgmigrate/issues/10, which was
caused by https://github.com/peterldowns/pgmigrate/pull/13.

When I updated pgmigrate to start using a fully-qualified table name
(schema.tablename), I had to update the implementation to use a new
helper for referring to the migrations table:
`pgtools.QuoteTableAndSchema`. Because there were no tests for the
migrator ops commands, I forgot to update their implementations as well,
resulting in them all failing due to table-name quoting problems.

This PR:
- Adds tests for the migrator ops commands.
- Fixes the migrator ops commands by switching to
`pgtools.QuoteTableAndSchema`
- Also updates the migrator ops commands to *ensure* that a migrations
table exists when they run, which will create the migrations table if it
didn't already exist. This is a change in behavior; previously, if the
migrations table didn't exist, the migrator ops commands would fail with
an error. I can't remember why I made that decision and I believe that
this is more user-friendly behavior.