fixed tearDown function

using Future.wait() now
added better check for api key
fixed encoding problems in service
Created generic ResourceCollection
created plan resource

also added basic tests
Added card to customer test
Removed alternative

comments will be added to explain the many exceptions and rules which
apply to the requirement of fields
Implemented coupon

added coupon collection and tests
Added customer documentation
Moved coupon tests into group
Implemented discount resource
Added coverage to full customer test
Added comment to abstract ResourceCollection
Renamed CustomerCardCollection to CardCollection
Fixed documentation issues
Extended plan
Extended subscription
Added subscription collection
Added trialEndNow for CustomerCreation
Added update to service