Whitespace
Cleaning up
Need to expose multiline arg as well as name

This is for the mappings in Cucumber's front-end, I learned this from
the spike.

I don't like exposing all these attributes. I wonder if we should be
pushing responsibility for talking to the mappings back to the test
step.
Adding a focussed test for the Mapper

Some thoughts / comments:

* I renamed some of the method calls (e.g. on the mappings)
  so we could use the describe_to methods.
* Renamed some others to try to standardise the language from
  define -> map. Not sure I'm entirely comfortable with it yet.
* The test feels horrible! I haven't had time to refactor it
  or listen to what it's telling us about the design, but it
  seems like it should have been easier to write a test
  around this object. Why wasn't it?
* We haven't actually proved in the test that the steps have
  been mapped - that you can now execute them.