Add PagoFacil gateway

http://www.pagofacil.net/

Closes #1054.
Fix failing remote test.
Initial commit of eWay Rapid 3.1 changes.

I've rewritten this to use the new JSON API.  I also removed the sandbox
credentials from the shared fixtures.yml since this was tied to a
specific eWay sandbox account and these credentials do not support the
new 3.1 direct transactions.
Finish eway rapid 3.1 gateway.

Finish refund implementation.  Add unit tests. Update rdocs.