Combined webos and touchpad detection, added flag silk, updated readme

Hi!

This time I've combined touchpad and webos detection (because they are basically the same). I've added the flag `touchpad` to webos detection if a touchpad is actually detected to preserve backward compatibility.

I've added the flag `silk` for Amazon Kindle devices.

Finally, I've improved documentation in the readme file to better describe available flags and fields. Still not perfect but better in my opinion.