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/misc/ccache/default.nix

@@ -38,7 +38,7 @@ stdenv.mkDerivation {
   };
 
   meta = {
-    description = "ccache, a tool that caches compilation results.";
+    description = "Compiler cache for fast recompilation of C/C++ code";
     homepage = http://ccache.samba.org/;
     license = "GPL";
   };