Fix address validator RegExp

Adds support for dashes in the address validator method.

Publishable keys

A new authorization method was added to the library to enable access to publishable keys in Rebilly:

// use this instead of setAuth
Rebilly.setPublishableKey('pk_.....');

You can create publishable keys in Rebilly here: https://app.rebilly.com/api-keys.
Documentation to follow in a patch.

Rebilly CDN

Updated the documentation to reflect the new Rebilly CDN as a provider for the library going forward.