Merge pull request #49 from stripe/cos-fraud

Cos fraud
Add FileUpload

* adds uploads.stripe.com endpoint
* adds support for multipart content
* some interface changes since we now have multiple backends
* bump to 4.0.0 since this is breaking
remove extra whitespace
switch from map to struct
Merge pull request #48 from stripe/cos-multipart

Add FileUpload
Add one-liner that sets the stripe key when running make test

This way, your STRIPE_KEY isn't kept in your shell after running.
Merge pull request #50 from stripe/shale/readme-with-test-example

Add one-liner that sets the stripe key when running make test
statement_description => statement_descriptor
Bump to 4.1.0
Merge pull request #51 from stripe/michelle-stmt-desc

statement_description => statement_descriptor
bump go version
Add IdempotencyKey to Params
Add headers to all invocations of c.B.Call
Unix -> UnixNano
Remove error from GenerateIdempotencyKey method
Remove the UnSetIdepmotencyKey method
Remove un-setting the idempotency key.