Removes simple and paypal examples

- These have moved to the recurly-js-examples repo
- The others should move there as well, in time

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adds pricing subtree observation for rebinding

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adapts pricing.attach to use OOP pattern

pricing.attach is now a factory for the local Attachment object prototype

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>