Add public domain "Fixed" font?

[trevorld]

• Could be used for testing monobit import #32 and/or provide more built-in options
• Available as "bdf": https://www.cl.cam.ac.uk/~mgk25/ucs-fonts.html
• Available as "fon": https://www.chiark.greenend.org.uk/~sgtatham/fonts/
• Available as "fnt": http://rasher.dk/rockbox/fonts/misc/