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/tools/misc/ncdu/default.nix

@@ -12,7 +12,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ ncurses ];
 
   meta = {
-    description = "An ncurses disk usage analyzer.";
+    description = "Ncurses disk usage analyzer";
     homepage = http://dev.yorhel.nl/ncdu;
     license = stdenv.lib.licenses.mit;
     platforms = stdenv.lib.platforms.all;