Support multiple subscriptions

Change Customer object to contain subscriptions and subscription
since customers can now have multiple subscriptions.

Change test to use subscription id for delete_subscription calls.
Finish supporting multiple subscriptions
Add flag debug_network

Add debug_network flag which allows the HTTPS request and response
data to be shown for debugging purposes.
Add interval_count to plans.

Add interval_count to Net::Stripe::Plan.

Fix missing module.
Add support for statement_description in plans.
Merge pull request #1 from rustyconover/master

Latest work on fixing up the module