[aprssig] Escaping \r\n in packets for APRS-IS

[John Langner WB2OSZ]

What should an RF to IS IGate do about \r (carriage return) and \n (line
feed) characters in packets?   The APRS-IS protocol uses \r\n as a record
terminator so having those characters in the payload would cause problems.

http://www.aprs-is.net/Specification.aspx  doesn't mention how to handle
this situation.

http://wiki.ham.fi/APRS_iGate_properties (no longer there) said:

"All packets sent to APRS-IS network are text lines ending with CR/LF
character pair. If the packet received from radio has CR or LF characters,
the packet is to be cut at first such character, and always a CF/LF pair is
appended for transmission to the APRS-IS."

https://github.com/hessu/aprsc/blob/master/doc/IGATE-HINTS.md  also
clarifies what should be done in this situation.  

The IGate should remove any \r or \n and anything following, from the packet
received over the radio, before passing it along to the APRS-IS servers.