Update jQuery, Font Awesome and Bootstrap JS version used.
Fix `head` meta properties order.
Minor cleanup.
Fix the remaining Bootlint errors.
Switch to `fa-3x` for the MaxCDN icon.
Tweak `script`s order.

Move Twitter script in index.jade. It's only used there so it doesn't make sense to include it in all pages. Also specify `async`.
Update GitHub link.
Fix typos.
.gitignore: sort entries.
Merge pull request #359 from XhmikosR/develop

Minor tweaks