GitHub – How to Export or Publish a File on GitHub

Yes, it is possible to have multiple GitHub Pages sites within one account. Create another GitHub repository and push your site files to the gh-pages branch. This would result in the site being hosted at tshepang.github.io/<repo-name>.

Now, push another file "CNAME" to the same repository and branch and fill it with movies.tshepang.net. Log in to your DNS host and add the CNAME to point to "tshepang.github.io" (just like the original site).

This would allow you to have seemingly two different sites on different domains. This would not work for having two or more sub-domains within github.io itself.

If the search engine crawlers honour the robots.txt then no, you won't be able to use external search engines to search for code hosted on GitHub.

Here's the line from their robots.txt file disallowing that:

Disallow: /*/*/blob/*

If you go jumping about repos you'll see the path to the source code is something like this:

https://github.com/asciidoctor/asciidoctor/blob/master/lib/asciidoctor.rb

This matches the rule and thus, you won't get anything back when using compliant search engines.