Empty skeleton.
The first failing test.

* I already know that I want my test fixtures to be slicing up
  a collection of colored shape models.
* I already know what interface I want to create a faceted
  collection: facets.facetCollection(criteriaFn, collection)
  A _criteria function_ is a function that takes a model and
  returns facet data for it.  For example if we are faceting
  by color, it will take a red square and return an id 'red' and
  the title 'Red'.
Make the first test pass.

* This is a very stupid way to make the first test pass, but
  there will be a lot of complicated behavior coming up and
  I want to make sure that I spent my time working on harder
  code when there are more tests to give me feedback.