Embed fonts instead of linking with dzslides-fonts

[galderz]

With dzslides, you can define the fonts to use, e.g:

:dzslides-fonts: family=Neuton:400,700,800,400italic|Cedarville+Cursive

This results in a link like this:

<link rel="stylesheet" href="http://fonts.googleapis.com/css?family=Neuton:400,700,800,400italic|Cedarville+Cursive" />

Would it be possible to have it by default download the font and link it locally or embed it?

Alternatively, if linkcss is passed, it should link to it, as it does now.

This would be useful for when the presentation is given offline.

[mojavelinux]

I've started to implement this. You can see the logic here:

https://github.com/asciidoctor/asciidoctor-backends/blob/master/slim/dzslides/document.html.slim#L27

We would just need something similar for the fonts. However, what makes it challenging for the Google Web Fonts is that that URL resolves to dynamically generated CSS file that depends on the user agent. The user agent for the script isn't going to be a browser, so you are going to get a different font file than what is optimal for the browser. I'm looking for a reference that explains how best to handle this situation.