More description fixes

* Remove package name
* Start with upper case letter
* Remove trailing period

Also reword some descriptions and move some long descriptions to
longDescription.

I'm not touching generated packages.

pkgs/development/libraries/tinyxml/2.6.2.nix

@@ -58,7 +58,7 @@ in stdenv.mkDerivation {
   '';
   
   meta = {
-    description = "TinyXML is a simple, small, C++ XML parser that can be easily integrating into other programs.";
+    description = "Simple, small, C++ XML parser that can be easily integrating into other programs";
     homepage = "http://www.grinninglizard.com/tinyxml/index.html";
     license = "free-non-copyleft";
   };