New port: comms/redsea

redsea is a lightweight command-line decoder for broadcast FM-RDS data,
such as that provided from a software-defined radio (SDR). It can also
decode raw ASCII bitstreams, the hex format provided by RDS Spy, and audio
files containing multiplex signals. Decoded RDS groups are printed to the
terminal as line-delimited JSON objects; optionally, undecoded hex blocks
can be output instead.

This program is intended to be used in combination with a separate source
of demodulated FM multiplex signals, such as rtl-sdr.

WWW: https://github.com/windytan/redsea/

PR: 234726
Submitted by: Andrew <morrand276@gmail.com>
Approved by: miwi (mentor)
Differential Revision: https://reviews.freebsd.org/D19164