add recipe for mpg123, a decoder for MPEG-1 layer 1, 2, and 3

mpg123 consists of a decoder library, and a command line application.
The application can be used to playback and dump decoded mp1/mp2/mp3 files.
The library can be integrated in other applications. CPU usage is minimal.

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>