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/tools/security/volatility/default.nix

@@ -16,7 +16,7 @@ buildPythonApplication rec {
 
   meta = with stdenv.lib; {
     homepage = https://code.google.com/p/volatility;
-    description = "advanced memory forensics framework";
+    description = "Advanced memory forensics framework";
     maintainers = with maintainers; [ bosu ];
     license = stdenv.lib.licenses.gpl2Plus;
   };