Create initializer with private attr_readers easily
Start using `Cucumber::Initialize`
Ensure we can make readers public
Rename Cucumber.Initialize to Cucumber.initializer
Merge branch 'initialize'

* initialize:
  Rename Cucumber.Initialize to Cucumber.initializer
  Ensure we can make readers public
  Start using `Cucumber::Initialize`
  Create initializer with private attr_readers easily
Use the mappings to run steps!

We need to build mappings to wrap the current cucumber runtime, and execute
steps for real.
Working towards a simple executable