feature request: externalize font files

[tantau]

In a multi-page svg document, move the font specifications to a separate file and link to them in each svg page.

Background: The pgfmanual is a 1150 page document that needs some 600 MB (!) of disk space as a sequence of 1150 svg's. About half of this space is taken up by the glyph outlines, which are repeated in each page. It would be a _HUGE_ improvement, if the fonts were put in a separate file and then just linked in each svg page.

[mgieseki]

This is already on my to-do list. I agree that it would be a huge improvement but it's also a huge amount of work that I can't afford at the moment. Instead of externalizing SVG fonts, I'd rather create corresponding woff/woff2 files on the fly.