Braintree

* Added Customer search
* Added dynamic descriptors to Subscriptions and Transactions
* Added level 2 fields to Transactions:
* tax_amount
* tax_exempt
* purchase_order_number

* Added billing_address_id to allowed parameters for credit cards create and update
* Allow searching on subscriptions that are currently in a trial period using in_trial_period

* Added ability to perform multiple partial refunds on Transactions
* Deprecated Transaction refund_id in favor of refund_ids
* Added revert_subscription_on_proration_failure flag to Subscription update that specifies how a Subscription should react to a failed proration charge
* Deprecated Subscription next_bill_amount in favor of next_billing_period_amount
* Added pycurl dependency in place of M2Crypto for better cross-platform compatibility
* Added new fields to Subscription:
* balance
* paid_through_date
* next_billing_period_amount

* Added AddOns/Discounts
* Enhanced Subscription search
* Enhanced Transaction search
* Added constants for CreditCardVerification statuses
* Added Expired and Pending statuses to Subscription
* Allowed prorate_charges to be specified on Subscription update
* Allowed argument lists and literal lists when searching for Subscriptions and Transactions
* Added AddOn/Discount details to Transactions that were created from a Subscription
* All Braintree exceptions now inherit from BraintreeError superclass
* Removed 13 digit Visa Sandbox Credit Card number and replaced it with a 16 digit Visa
* Made gateway operations threadsafe when using multiple configurations
* Added new fields to Subscription:
* billing_day_of_month
* days_past_due
* first_billing_date
* never_expires
* number_of_billing_cycles

* Added support for M2Crypto version 0.20.1, which is the default for Ubuntu Lucid (thanks [foresto](https://github.com/foresto))

* Added unified message to ErrorResult
* Added ability to specify country using country_name, country_code_alpha2, country_code_alpha3, or country_code_numeric (see [ISO_3166-1](https://en.wikipedia.org/wiki/ISO_3166-1))
* Renamed Subscription retryCharge to retry_charge
* Added gateway_rejection_reason to Transaction and Verification
* Allow searching with date objects (in addition to datetime)
* When creating a Subscription, return failed transaction on the ErrorResult if the initial transaction is not successful