Bump for release v1.32.1
Netaxept: Revamp to use the "M" service type

The previous implementation used a Netaxept "service type" that they
don't like to give customers access to. This completely revamps the
gateway to use the actually accessible service type.

Closes #581.
Litle: Void authorizations via an auth reversal

This changes the format of the authorization string, but the change
should be fully backwards compatible with any already stored
authorizations.

Closes #642.
Add RBK Money integration

https://rbkmoney.ru/

Closes #647.
Direcpay: Update test url

Closes #651.
PayPal Express gateway: Add billing agreements

It's now possible to create a billing agreement without actually running
a full transaction. Uses the #store API.

Closes #605.
RBK Money: Fix user_fields for 1.8
Litle: Fix for Rubinius

Rubinius' behavior around returning an array is subtly different, and
my oversight with regards to not explicitly building the array to return
in split_authorization tripped it up.
PayPal Express gateway: Add reference auths

Closes #652.
Add CardStream Modern gateway

This integrates the latest API from Cardstream and adds the ability to
authorize, capture, refund and void transactions. The gateway is called
CardStreamModern to avoid confusion. Modern is a made up name,
Cardstream themselves call the latest version Cardstream and the early
version legacy.

Closes #595.
Pin: Really pass special headers

My previous commit around this functionality was actually not passing
the special headers like it was supposed to.
(5dc3bd5c78470068eda1af098e14d6d255f6fa82)

This commit fixes the previous careless attempt and adjusts things such
that we're now actually testing that the right headers get passed rather
than just testing that the right headers are created.

Closes #654.
Paypal Express gateway: Remember billing agreement

The Paypal Express #store method uses Paypal's CreateBillingAgreement
API call.  The response to this call gives us the billing_agreement_id
which can then be used for future charges via the DoReferenceTransaction
API call.

This commit allows us to consistently ask the response for its
authorization.

https://www.x.com/developers/paypal/documentation-tools/api/createbillingagreement-api-operation-nvp

Closes #656.
Paypal Express gateway: Allow an amount of 0

No longer default the amount to a dollar.  There are times when an
amount of 0 is perfectly fine for a Paypal Express transaction.

In fact, an amount of 0 is required if you'd like to do an authorization
without an immediate charge.

https://www.x.com/developers/paypal/documentation-tools/express-checkout/integration-guide/ECReferenceTxns

Closes #655.
Paypal Express gateway: Reduce param requirements

For reference transactions, Paypal Express does not require a payment
type, an invoice_id, a description, or an IP.  We shouldn't require them
either.

They can certainly be specified and we pass them to Paypal
appropriately, but they're not required.

Closes #657.
Quickpay integration: Update to handle API v6

Fixed that the quickpay notification parser failed to parse v6
notifications both because they are now URL-form encoded (since v4), and
because it was missing two fields in the checksum calculation

Closes #658.
Add 2.0.0 support at travis-ci, and allow failure
Merge pull request #663 from sanemat/feature/travis-ruby-2-0

Add 2.0.0 support at travis-ci, and allow failure
Sage gateway: Deprecate #credit call

Use #refund instead.

Closes #666.
Update notification generator

Notification template's parse method is a bit outdated. This is to make
it in sync with latest notification class. I also documented that fact
that notification initialization requires raw post string.

Closes #664.
Swap out REXML for Nokogiri in payflow common parser.

REXML is very strict with its xml parsing so fails hard on invalid
characters, Nokogiri strips them and continues on. This is a much better
experience for ActiveMerchant users.

I've only replaced the parser in Payflow common, but we should work on
moving everything to Nokogiri since it is a much better XML parser.