Copy button for code blocks

[pfitzseb]

Fixes #1055.

[fredrikekre]

I think it looks better with a copy icon like in #1454 instead of Copy

[pfitzseb]

Fair.

[fredrikekre]

Could the button be added only if javascript is enabled (i.e. at "runtime")? I did that here https://github.com/fredrikekre/fredrikekre.se/blob/master/_libs/clipboard.js for example. The way I did it there I don't need to do any unescaping, or include the code twice (once printed without colors as you do here IIUC). But maybe thats just because I used https://clipboardjs.com/ which handles that for me? Any reason not to use that?

[pfitzseb]

Sure, we can do that as well.

[fredrikekre]

Nice, add a changelog entry?

[fredrikekre]

Something buggy with the icons using the dark theme? I see this:

for example (firefox, macos).

[fredrikekre]

Ah, looks like a CSS problem. In the dark theme font-family is overridden so it is missing font-family: "Font Awesome 5 Free";

[pfitzseb]