Consider using non-proprietary fonts

[tingerrr]

Consider using a free equivalent for the proprietary font fallbacks use in the default config.

Especially in CI, where one would usually generate documentation automatically, installing fonts is a pain when they're not free. In general, the default theme should not assume a proprietary font is or can be installed, even if it is just a fallback.

A very dead-on free equivalent to Helvetica is Tex Gyre Heros.

[jneug]

Seems easy enough.