Improve assertions feature
Improve getting started feature
Improve background feature
Simplify features
Organise features into folders
Strict build so it fails on undefined steps
Move over one legacy feature
New directory structure for Cucumber's own features

Now that the features are organised into sub-folders,
I was getting confused between the `support` and `step_definitions`
folders and the actual feature sub-folders.

I think this directory structure makes more sense as I can
clearly see which files are documentation and which are glue
code.
Migrate over legacy feature

Note that I had to add the spawn tag. I guess this is because
we don't clear out enough state about hooks perhaps?
Delete legacy low-level feature
Migrate over another two legacy features
Ooops
Remove Ruby 1.8.7 complectification
Actually run the legacy features again #408
Move aruba require back into support/env.rb

Shame, because this means you can't use --dry-run, but
otherwise tests are failing.
Remove Ruby 1.8.7 code
`Given` method for calling steps is deprecated.
Merge branch 'master' into turn-ast-inside-out