Complete query_delivery_status to request with sender
Add model class for subscription to notifications
Add subscribe/unsubscribe to notifications functions in SmsClient class
Add support for JSON in execute_request HTTP python class
Add support for JSON
Update send message example with JSON support
Add example for subscribe/unsubscribe to notifications
Update example with argparse module

Signed-off-by: Julien Richefeu <julien.richefeu@intersec.com>
v0.02 - added default data_format, model mapping fixes, minor improvements
added comments and TODOs