Added a method to send a CreateBillingAgreement request
Created an "advanced" section of documentation for PayPalWPP
 * Copied the basic descriptions from PayPal's NVP documentation pages https://developer.paypal.com/docs/classic/api/
 * Provided a basic example of createBillingAgreement
Added a test for createBillingAgreement
This is my first test using mock. Please be gentle.
Added another assertion for a CreateBillingAgreement error
Rewrote runtests.py to be more modern and standard
Fixed missing dependency in tox.ini
Merged pull request 42, with related changes.