Version 0.2: simplification and clarification

[martinpaljak]

Address #14: Only a single APDU at a time can be exchanged over BLE (as a SE can only process a single command at a time) and the responsibility of GET RESPONSE handling is clarified Address #7: one level of wrapping and related packet overhead is removed by addressing #14 Address #13: recommend re-sending the notification if response is not read in a timely fashion Address #11: have the response notify include an error code

Further reduction of the overhead in payload headers should be considered.