Remove stuff we no longer need.

Translation: almost everything.  This clears out some space for us to
add support for the main Spreedly API:

https://core.spreedly.com/manual
Start on some plumbing

Made some progress on the find_payment_method api call support.  This is
driving support for some of underlying https interactions.

The approach has much in common with Active Merchant.  In fact a good
bit of it is simply copied and potentially simplified for our use.

Much more work to do.
Simplify ResponseError a bit
Expose payment method errors
Ignore tmp dir
Some README driven development
Cleanup readme
Improve the readme more
Add some error handling to readme
Improve error message handling

Improve handling of Authentication errors and Not Found errors.
Environment has a default currency_code
Support full_name in credit card
Flesh out purchase call a bit

Laying some groundwork, looking at response codes, handling the basics
for the sample app.

Still have cleanup to do, tests to write, and doing things more 'right'.
Start adjusting test responsibilities

Remote tests are responsible for testing the very basics:

* The connection is made.
* The right type of object is returned.
* An attribute or two of that object has been filled.

Then unit tests can mock out the response and more thoroughly test that
all of the details are filled out in the returned object.

This is similar to how ActiveMerchant does some of its testing.
Use Github markdown more effectively

Syntax highlighting FTW!
Fix typo
Fix another typo
Handle 402 (Payment Required)
Start on add payment method

Just a start on some of the pieces to be used by some of the remote
tests.  There are tasks out there in GH issues to flesh this out fully
with tests, etc.
Refactor where response parsing happens

This is an attempt to make model specific response parsing easier and
ensure that parsing doesn't happen more than once for a response and we
don't have weird parsing of sub responses.