Make packetize block produce text output.

Each line is a comma-separated list of values terminated by CR/LF:

$FLM,<iso-date>,<rxid>,<channel>,<icao>,<lat>,<lon>,<altitude>,<raw_hex>

$FLM       - fixed packet identifier
<iso-date> - The current date and time formatted according to ISO 8601
<rxid>     - The receiver ID, which is normally a one-byte hex value
<channel>  - The channel (0-64 in North America) on which the packet was received
<icao>     - The ICAO 24-bit aircraft ID in hex
<lat>      - The GPS latitude in 10000000ths of a degree. North is positive.
<lon>      - The GPS longitude in 10000000ths of a degree. East is positive.
<altitude> - The GPS altitude
<raw_hex>  - The 29 raw bytes of the packet in hex, including Nordic address & CRC