Add Checkmark On visited Links

[Xipas]

Added the missing code to show the checkmark on visited links on sidebar. All js code was already in place, just missing some html.

[matcornic]

Many thanks @Xipas for your PR :)

I did not implemented this functionality because, personally, I did not find it useful. But other people (like you 😋) do.

So, can you add an optional boolean showVisitedLinks parameter like this ? Then use .Site.Params.showVisitedLinks in the Go Template.

Thank you for your understanding.

[Xipas]

Done :)

[Xipas]

Added a css code to set color and align to right.

[matcornic]

Updated the doc as well : https://matcornic.github.io/hugo-learn-doc/basics/configuration/

[matcornic]

@Xipas Did not see it at the first time, but if we define an font awesome icon in the prefix of a menu item, it's not shown. We should add a class for the check icon, in order to be specific.

[matcornic]

@Xipas I added a comment on the code of your PR. I got a regression when I used Font Awesome icons as prefix for the menu (ex in front matter of a chapter page : icon: "<i class='fa fa-users'></i>")

[matcornic]

@Xipas it's fixed in de8584e