mpg123 decoder...

[Ryan C. Gordon]

...I just committed a libmpg123-based decoder to revision control, and 
removed the smpeg and mpglib decoders. libmpg123 is basically a 
very-much improved version of mpglib anyhow.

You don't need to accept lousy tradeoffs between the two decoders any 
more, nor require an external library. The new decoder has all the 
functionality of both decoders and none of the limitations. Unlike 
mpglib, this decoder seems to play mp3s that were recorded after 1999, 
too.   :)

The code is very new, but already works pretty well, so go ahead and 
play around with it.

 From the configure script, --enable-mpg123 (defaults to enabled), and 
then use SDL_sound as you normally would.

I haven't updated any of the other project files besides the configure 
script. I'll probably be removing them for CMake or something soon anyhow.

--ryan.