Use gh-pages for GitHub pages

[Falci]

I was working on #81 and then I realised we can do some improvements in the structure of this repo.

Here's my suggestion:
First, separate source and auto generated files. Currently, the build generates files in the repo's root (index.html).
The build script does a surgery for cleaning the workspace before generating new files.
We could have a single ./build folder and use that as root for GitHub Pages.

Since the final goal is to automatise the doc generation, we could go even further and use another branch. This is a common strategy. We have a branch in which we only have the website content, all generated files, plus any other resource. No sources there.

The main advantage on having a separated branch instead of a folder is the event: when using different branches a change in master always means new/updated content and can trigger the docs generation which will push changes to a side branch

So, the first step in this direction would be to create a branch from master, named gh-pages and update this project settings to use that branch as source for GitHub Pages.
I can't create a PR to a non-existing branch, nor change the repo settings.

[pinheadmz]

new branch: https://github.com/handshake-org/handshake-org.github.io/tree/gh-pages