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