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/development/libraries/audiofile/default.nix

@@ -11,7 +11,7 @@ stdenv.mkDerivation rec {
   };
 
   meta = with stdenv.lib; {
-    description = "A library for reading and writing audio files in various formats";
+    description = "Library for reading and writing audio files in various formats";
     homepage    = http://www.68k.org/~michael/audiofile/; 
     license     = licenses.lgpl21Plus;
     maintainers = with maintainers; [ lovek323 shlevy ];