Some description fixes

There are many more packages to fix, this is just a start.

Rules:
 * Don't repeat the package name (not always that easy...)
 * Start with capital letter
 * Don't end with full stop
 * Don't start with "The ..." or "A ..."

I've also added descriptions to some packages and rewritten others.

pkgs/applications/audio/audacious/default.nix

@@ -49,7 +49,7 @@ stdenv.mkDerivation {
   enableParallelBuilding = true;
 
   meta = {
-    description = "Audacious, a media player forked from the Beep Media Player, which was itself an XMMS fork";
+    description = "Audio player";
     homepage = http://audacious-media-player.org/;
     maintainers = with stdenv.lib.maintainers; [ eelco simons ];
     platforms = stdenv.lib.platforms.linux;