There are four assistant roles:

creator (``create`` or ``crt`` on command line)
  creates new projects
tweak (``tweak`` or ``twk`` on command line)
  works with existing projects
preparer (``prepare`` or ``prep`` on command line)
  prepares environment for development of upstream projects
extras (``extras`` or ``extra`` on command line)
  performs arbitrary tasks not related to a specific project

The main purpose of having roles is separating different types of tasks.
It would be confusing to have e.g. ``python django`` assistant (that
creates new project) side-by-side with ``eclipse`` assistant (that registers
existing project into Eclipse).
