Merged r8195:8205 from jcorgan/ecc into trunk. Adds convolutional encoder

Merged r8195:8205 from jcorgan/ecc into trunk.  Adds convolutional encoder
and decoder corresponding to the R=1/2, K=7 CCSDS standard ("Voyager").

This code is a GNU Radio wrapper around a 1995-era KA9Q portable-C
implementation, and is designed for continuous streaming data, not packets.

The encoder takes MSB packed bytes and outputs channel symbols 0 or 1.

The decoder uses soft-decision Viterbi decoding on a floating point stream of
(possibly noise corrupted) [1.0, 1.0] symbols, and outputs MSB packed
decoded bytes.

Benchmarking on a 2.16 GHz Intel Core 2 Duo shows 4.7 Mbps decoding rate at
100% CPU usage (single core).  (There is a newer KA9Q library that implements
SIMD speed ups with correspondingly faster performance.)

The KA9Q library is placed into src/lib/viterbi.  It could use some cleanup,
file/function renaming, and refactoring, or even replacement with the newer
libfec code that is available.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@8206 221aa14e-8319-0410-a670-987f0aec2ac5