Add partial (or fuzzy) search for the module name in the mix task `spirit.gen`

As a QoL improvement: if a wrong name is provided as an arg to `mix spirit.gen`, instead of printing the entire list of module names, we could only print those that might be close matches to the given arg.

A simple partial (substring) match is the easiest to add. But maybe we can get fancy with a string distance metric or something similar.