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/tools/build-managers/apache-ant/default.nix

@@ -23,4 +23,8 @@ stdenv.mkDerivation {
     url = "mirror://apache/ant/binaries/apache-ant-${version}-bin.tar.bz2";
     sha1 = "d9e3e83dd9664cfe1dcd4841c082db3f559af922";
   };
+
+  meta = {
+    description = "Java-based build tool";
+  };
 }