KNX cEMI Server

Implementation Notes

currently only implemented for KNX USB Data Interface (Tunnel) and not KNXnet/IP for now
basically provides a complete KNX device (TP or RF) that also has a USB interface built-in which can be used to program either the local device stack or remote devices via the attached medium (TP or RF).
- tested with ETS 5.7.x
- tested with Net'N'Node
- Be careful when using this with TP as your HW setup might not have a galvanic isolation between the KNX bus and USB!
  - An USB isolator might be the easiest option. Not tested!
  - ToDo: How is this realized in commercial KNX USB Data Interfaces?
cEMI client address (e.g. ETS) is based on KNX physical address of the local device stack +1
- Example: local device: 1.2.10 -> cEMI client address: 1.2.11
- PropertyWrite commands to change the cEMI client address are only temporary until next device restart
requires a USB stack which properly work with USB HID and provides interrupt IN/OUT endpoints for KNX HID reports.
- normal Arduino USB device stack does NOT work as it is missing required functionality
- TinyUSB stack is used instead, therefore the Adafruit SAMD core with TinyUSB enabled is used as the Arduino core