Docs: Consider moving Docs into /docs directory instead of gh-pages branch

[ericrallen]

It's much easier to keep Documentation and Source Code in sync when they are easily viewable at the same time and PRs that address changes in one can update the other.

GitHub supports using the /docs folder in your master branch as the source for GitHub Pages and I'm not very familiar with gitbook, but it seems like there might be a configuration tweak to support the same-branch setup.

This would mean that new work that isn't quite ready to be part of the live documentation would need to be merged into a develop branch first or that a release/ branch would need to be used until the new changes are ready to be published as a release.