Paypal

-----

* Replaced iteritems() with iter() for Python 3 compat. (brutasse)
* A few README fixes. (brutasse)

-----

* Adjusted imports to be compatible with Python 3. (ibrahimsag)

-----

* Removed handled exception error logging. Cuts down on spam. (ibrahimsag)
* Some assorted PEP8 fixes. (gtaylor)

-----
* Added ``useraction`` parameter to Express Checkout URL generation
* Raise PayPalConfigError on call attempt with None values for configurations

-----
* Added support for RefundTransaction. (cbsmith)
* Migrated from ancient 72.0 API_VERSION to 98.0 API_VERSION. (cbsmith)
* Style guide compliance updates (some pep8 and pyflakes love). (cbsmith)
* Use POST instead of GET for NVP API to avoid GET length limits. (marcbelmont)
* Obscure API credentials in logged error messages. (davidfooks)
* Various PEP8'ification and cleanup. (oczkers)
* BIC: Python 2.5 is no longer officially supported. Time to move on, folks.

-----

* Minimum supported Python version is now 2.6. It may still work with
Python 2.5, but I am not hugely interested in maintaining support. Pull
requests are accepted, of course, but breakages in future releases may happen,
because I won't be testing against 2.5.
* Replacing urllib2 with python-requests. Greatly simplifies things, and
improves SSL certificate validation.
* Preliminary (potentially rough) Python 3 support.
* SSL certificate validation is now enabled by default. The old behvaior of
being able to specify a private cert to validate against still remains.
* Tests are now ran via nose. The old test runner is no more. See the README
in the ``tests`` directory for details.
* Added the ``bm_create_button`` method, which maps to BMCreateButton.
* UniPay should be working again.
* All of the PayPal exceptions now correctly call Exception.__init__. This will
prevent some edge cases with those using something like Sentry for error
reporting.
* Improved the settings module logic. Also added validation to make sure
correct settings are being passed in.