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/mediastreamer/default.nix

@@ -36,7 +36,7 @@ stdenv.mkDerivation rec {
   NIX_CFLAGS_COMPILE = "-Wno-error=deprecated-declarations";
 
   meta = with stdenv.lib; {
-    description = "a powerful and lightweight streaming engine specialized for voice/video telephony applications";
+    description = "A powerful and lightweight streaming engine specialized for voice/video telephony applications";
     homepage = http://www.linphone.org/technical-corner/mediastreamer2/overview;
     license = licenses.gpl2;
     platforms = platforms.linux;