* Converted CharacteristicDeclaration implementation to class
* Added ability to get a gatt_server attribute by service UUID, characteristics UUID, descriptor UUID
If characteristic supports Notify and Indicate, the prefer_notify option
will subscribe with Notify if True or Indicate if False.
If characteristic only supports one property, Notify or Indicate, that
mode will be selected, regardless of the prefer_notify setting.
Tested with a characteristic that supports both Notify and Indicate and
verified that prefer_notify sets the desired mode.
Subscribe command will enable notify or indicate events from the
characteristic, depending on supported characteristic properties, and
print received values to the output window.
Unsubscribe will stop notify or indicate events.
Rename find_attribute() to find_characteristic() and return a
characteristic for a set of UUIDS, a characteristic for an attribute
handle, or None.
Print read and received values has a hex string.
Add an unsubscribe implementation to gatt_client.py. Reset the CCCD bits
to 0x0000. Remove a matching subsciber, if one is provided. Otherwise
remove all subscribers for a characteristic, since no more notify or
indicates events will be comming.
authored-by: Michael Mogenson <mogenson@google.com>
