added payment module
added module to handle webhooks
added payment to attr_reader
added subscription_canceled to webhook
mark payment.get as not implemented
get is a class method.
user more descriptive names to set instance variables
use demo data
add hash to Customer
Customer.hash and Customer.changedata_url should not be an attr_accessor
add Subscription.hash to attr_accessor
add status to subscription
added hash to subscription
fixed webhook parsing
added more attr_accessor
Merge branch 'feature_webhooks' of https://github.com/easyPEP/fastbill-automatic into feature_webhooks

Conflicts:
	lib/fastbill-automatic/subscription.rb
add dunning level to payment
allow invoice limits
added FBA invoice attr_accessibles
fixed default attributes