Update catnav.html

Added a direct link to the Github. Currently, you'd have to go to a category and then to a script, and then click on the View on Github button to get there..

Modified the Godot Engine link text, as it isn't just a 3D game engine; in fact, it's stronger as a 2D engine at the moment and could be used to make apps/tools in addition to games. Also the /wp in the URL is unnecessary and would break if the site is updated to move to the webroot or a different directory, so may as well just let the domain redirect as needed.
fixed the link

I'm an idiot. If this is also wrong, it's too late and I'm too tired to be editing stuff in public. haha.
Merge pull request #6 from adolson/patch-1

Brilliant. Thanks for helping