take test values from environment, describe integration test setup in TESTING.md
rewrote package with proper design
move private method to bottom
update readme
move xml marshalling to braintree object
removed unnecessary parameter declarations
implement subscription api (partial)
implement plan api
don't expose methods that don't need to be public
moved types that have a distinct gateway to separate files
link to package docs
implement address create/delete
config obsolete, move data to braintree object; new environment type
if logger is set on braintree output requests are logged
Merge pull request #2 from eaigner/master

Rewrote package, partially implemented subscriptions. Fixes #1.