Fix HTTP/HTTPS links

[emilmelnikov]

• Restore PR #78
• Remove site.baseurl and other unneeded/old entries from config file: site.baseurl is a prefix that follows the host (e.g. in https://example.com/mysite/posts/hello, site.baseurl = mysite).
• Replace HTTP links with HTTPS where possible.
• Fix some internal anchor linking.
• Cleanup slides on the main page.