patch to add correct handling of APRS, used for pymultimonaprs and other possible iGate software

This patch adds a new option to multimonNG, which outputs correct (TNC2 formatted) APRS packets, instead of raw AX.25 frames in AFSK1200 mode.

run with "multimonNG -A" to get APRS format output.

Example output:

	APRS: DO1GL-5>APDR12,DO1GL*,WIDE2-2:=5111.11N/01111.11E$ http://aprsdroid.org/