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/games/blobby/default.nix

@@ -15,7 +15,7 @@ stdenv.mkDerivation rec {
   '';
 
   meta = {
-    description = ''A blobby volleyball game.'';
+    description = ''A blobby volleyball game'';
     license = with stdenv.lib.licenses; bsd3;
     platforms = with stdenv.lib.platforms; linux;
     maintainers = with stdenv.lib.maintainers; [raskin];