[STUMP] New Manual hosted on stumpwm.github.io

Hi All,

Just wanted to let you know that I've published an updated version of
the manual:
https://stumpwm.github.io/

In an ideal world, this will be updated with the head of git at all
times, but that rarely happens.

Eventually I would like to have an index with each stumpwm version and
git with their respective manuals.  This is good for now because it
provides an online version of the manual.

I also tweaked the css style quite a bit to make the format look
less... garish.  If anyone has more design experience and wants to play
with the css, its here:
https://github.com/stumpwm/stumpwm.github.io

Feel free to open pull requests or issues against this as long as it
pertains to the manual only!

Cheers,

    Dave