formatting. remove () from methods that don't have arguments
formatting. alphabetize key-values by keys and add comments.
rename internal variable. rename `new` to `new_hash` so it's not a Ruby keyword
Extract response helpers to module

Allow developers to use Stripe test data when stubbing responses
locally. This should help mitigate the risk of API drift with stubbed
responses.

* Move response helpers to their own file
Merge pull request #169 from harlow/hw-extract-helpers

Extract response helpers to module
Change `Helpers` to `Stripe::TestData`
Merge pull request #170 from westonplatter/formatting

Formatting. Just a few suggestions on code format.
Merge pull request #172 from westonplatter/rename-internal-var

rename internal variable. rename `new` to `new_hash` so it's not a keyword
Consistently use symbols for hash keys

* Updated keys to symbols to match the rest of the test helper