HoTT telemetry functionality

This one adds telemetry functionality to HoTT transmitters. This telemetry uses 19200 Baud with half duplex protocol. Because of there is no half duplex protocol available on modul level, RX and TX of the used USART have to linked with a resistor of 2k and the RX pin has to wired directly to the telemetry pin of the receiver. Later it is planned to wrap the half duplex functions upwards from PIOS to modul level. Then a wire from TX of USART to 'T' of the receiver will be enough.
The module emulates 5 sensors: VARIO,GPS,General, Electric Air and Air ESC. The sensors have configureable warning levels which can generate simple beeps or spoken messages on ground.