change drush commands to match drush core

Drush now has a standard form for commands: pm-download, cache-clear, sql-query, where the first part is the module (or Drush plugin) which provides the command. Commands may also have an abbreviated version.

We should match this pattern, so:

- mb-build (mb) -- build module code
- mb-list (hooks) -- list hooks
- mb-dl -- download hook data