Support multiple fonts in the text-font property array

[PetersonGIS]

Fresco should support the listing of multiple fonts in the text-font property. It does not throw an error when you attempt to do so but it will not render the tiles.

Here's what's happening in my use case:

This city label should show all the character glyphs so I want to add some fallback fonts:

Currently the code just has one font listed:

When I try to add another font so that I can add in some character glyphs, the tiles don't load:

The console reports a 404. I believe it might be looking for a font with a name that has both of those names combined instead of looking for each individual font. As a workaround I have considered combining all the fonts I need into a single font. However, it looks like I may run into a limitation in terms of how many glyphs can be in a single font so it would be better if I could use Fresco to add in fallback fonts.