Produce CSS in which local fonts are not used

[RLesur]

Hi @pvictor, @mfanny,

Thanks a lot for this beautiful gem (as usual 😉)!

This PR is a proposal to allow the user to remove the local source which is here:

gfonts/inst/assets/templates/css_best.txt

Line 7 in 7e921df

src: local('{variant$local[[1]][1]}'), local('{variant$local[[1]][2]}'),

In fact, I have some use cases in which I need to remove the precedence of user installed fonts over downloaded fonts:

• user installed font version is different than the downloaded font version. In this case, I want to force the use of the downloaded font and avoid the use of a local font. The goal is that the web page looks exactly the same for each user.
• self contained R Markdown documents: since the font is embedded in the document, the use of a local source is needless.

[pvictor]

Nice! Thanks for the explanation :)