Set up rake tasks to make running features easier

Three things here:

1. I'm going to translate features over, and mark them as failing when
they are failing. I'll also tag them with gh-N to mark GitHub issue #N
that they go along with.
2. `bin/rake cruise` has been set up to run for CI. Basically, it runs all
the things that aren't failing, and makes sure they pass. Then, it runs
all thet hings that are supposed to be failing, and makes sure they
fail. If either of those are not true, it fails the build, and if
they both pass, they pass. This way we know when something starts
passing again, and to remove the failing tag.
3. `bin/rake focus` is added when developing new scenarios. You just tag
the scenario you're working on with `@focus`, and then `bin/rake focus`
will run just that one scenario.
New feature: creating API keys.

There was no existing schemas for the API key response, so I made one.
New feature: retrieve API keys
New feature: list all API keys
New feature: remove API keys
Refactor/reorganize steps for clarity.

It's important not to refactor steps _too_ much, but these were certainly
http steps and not card steps.
Update README.
Adding technical documentation.
moving root_url and accept_headers into global variables
adding card tokens schema
Refactor schema error handling, reintroduce failure

We should handle these errors better, and now that we are,
let's reintroduce the failing second half of the scenario.

I'm actually not entirely sure that flunk-ing with the message
is any different than just bubbling up the error, but at least
it's a real assertion failure error, rather than a JSON API
parsing error.
basic create customer scenario
micro library to contain interaction with the api
New feature: Customer index
clean up some whitespace
New feature: get customer
'fix' failing address spec.

This was failing, but for the wrong reasons. Let's fail for the right ones.
Clean up some small formatting issues.

I missed these in my earlier cleanups.
New feature: remove a customer
New feature: create a callback