* Add comments to the Graph randomizer code

Modify the class attribute instead of the instance attribute.

* Use a dictionary for command assertion instead of one assertion per
  kv pair
* Explicitly check for the name "Commander"

* Reset object count and commands list to previous values
* Use dictionaries for all assertions rather than checking single keys
* Create a Commander object in setUp() for use with most tests

It reduces code redundancy by performing the common operations of
fetching the last command and constructing the command dictionary
from the given arguments.

* Add type alias equivalent to os.PathLike to support Python 3.5