feat: Publish gh-pages by site-deploy target in Makefile

[dakusui]

Hi!
This is a pull request to add a gh-page based documentation site.
You can deploy your web site by doing make-site-deploy.
The site will look like this: https://dakusui.github.io/insdog/ (Doesn't it look cool?)

Before trying this feature you need to create gh-pages branch on your remote GitHub repo by doing for example:

 git checkout --orphan gh-pages
 rm -fr ./* .idea/ .github/
 touch README.md
 git add README.md 
 git commit -a -m 'Initial commit'
 git push -u origin gh-pages:gh-pages

Also, please ensure your gh-pages is enabled. (I know your company's policy, but don't worry and don't forget InsDog is already open-sourced!)

[sukezan]

LGTM!
I tried it on my forked repo and confirmed that it works.