Sanitize, optimize, and a few bugfixes

[Pwuts]

The commit messages sum it up:

• sanitized main.css by removing all CSS shared/duplicated between Bootstrap and Bootstrap Grid
• removed random trailing whitespace from many files
• fixed and updated theme.js syntax
• updated and minified Lunr js file
• updated Bootstrap and JQuery js libraries
• removed local bootstrap.js file
• fixed author page links (broken in current release version)
• added GitHub+GitLab link support to author profiles
• added rel="noopener" to external links because good practice
• moved contact.md -> contact.html as it contains html and not markdown
• fixed crammed 404 page layout
• fixed excludes in _config.yml
• added a robots.txt file which includes the host instead of just /sitemap.xml

[Pwuts]

Is anything ever going to happen with this PR? I put quite some effort into making it neat and publishable :/

[aschrijver]

It is a real pity that this work was never considered, not even honored with a comment.

[Pwuts]

Bump; please check out this PR :)