Captialize meta.description of all packages

In line with the Nixpkgs manual.

A mechanical change, done with this command:

  find pkgs -name "*.nix" | \
      while read f; do \
          sed -e 's/description\s*=\s*"\([a-z]\)/description = "\u\1/' -i "$f"; \
      done

I manually skipped some:

* Descriptions starting with an abbreviation, a user name or package name
* Frequently generated expressions (haskell-packages.nix)

pkgs/development/libraries/minixml/default.nix

@@ -10,7 +10,7 @@ stdenv.mkDerivation  rec {
   };
 
   meta = with stdenv.lib; {
-    description = "a small XML library";
+    description = "A small XML library";
     homepage = http://www.minixml.org;
     license = licenses.lgpl2;
     platforms = platforms.linux;