Only LSB of batteryChargingCurrent is sent in RTTY

[jgromes]

Due to a cast from int16_t to uint8_t, only LSB of charging current is sent during RTTY system info transmission:

FOSSASAT-1/Code/FossaSat1/communication.cpp

Line 282 in e9ca4d4

Communication_RTTY_Print_Hex(batteryChragingCurrent);

Also, current RTTY system info prints out letter shift symbol at the end of each hex-encoded byte. This makes transmission longer than it needs to be (although easier to decode in some cases).