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/aubio/default.nix

@@ -16,7 +16,7 @@ stdenv.mkDerivation rec {
     ];
 
   meta = { 
-    description = "A library for audio labelling";
+    description = "Library for audio labelling";
     homepage = http://aubio.org/;
     license = "GPLv2";
     maintainers = [ stdenv.lib.maintainers.marcweber ];