Tweaks for https://github.com/killbilling/recurly-java-library/pull/38 before merge:

* Reduce visibility of doGET
* Remove StringBuilder
* Fix whitespace issues

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
model: add tokenId in BillingInfo

Reported-by: Seth Lee <sethwlee@gmail.com>
Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
Support CVV with leading zeroes

Trim whitespace from string values