Allow fonts to be specified / customized

[mojavelinux]

While it's possible to use custom epub3.css and epub3-css3-only.css files, it's not possible to override the epub3-fonts.css file and, with it, alternative fonts. It should be possible to override the fonts as well.

The way the packager works is that it scans the epub3-fonts.css file for font references and packages those fonts in the archive. Therefore, we we'll also need to honor the epub3-fontsdir property to control how these fonts are resolved.

[gdamore]

Yes PLEASE!

I hacked around this by copying my own fonts into the gem data directory, but there is also some stuff about this that needs to consider e.g. scripts setting, and of course it should pick up the fonts.css from the same place it picks up the style css.

I did notice that the packager also blithely copied fonts I didn't use or didn't need -- basically the builtin fonts get copied whether I want them or not.

[gdamore]

I see someone else has taken over maintenance it appears (@slonopotamus ) -- I still really really would like this! I definitely would like to supply my own fonts (the Ubuntu fonts in my case), and it's kind of a pain as I have to go back and figure out what I did like two years ago, as I'm getting ready to release a significantly updated edition.)

[znowacki]

As user, I will be grateful for that option. Standard fonts - when used for my language special letters , PL - look weird. I would even prefer not to have any included font than this issue.