Since a while, Hugo has its own mechanism for code highlightning.
We remove the old highlightning code provided by the client-side javascript library highlight.js and all its related files.
This also solves issues introduced by Hugos own highlightning because in our theme we are currently highlighting the code twice leading to unpredictiable results.
This will also fix an issue were light code highlightning themes weren't displayed correctly because our styles are overwriting color information.
Another advantage is the huge list of supported languages which by far exceeds our current list.
On the downside, this is a breaking change because our current color theme isn't supported by Hugo.
This is useful because using "alt" attribute is generally a good idea. But I had to change this in my project because I am running automated tests and this was causing an error from my over-zealous error-checker robot. Fair enough.
