Improve default fonts and support displaying all unicode characters

[kkoreilly]

Roboto, Roboto Mono, and the Noto Sans fonts should be embedded into apps by default. Roboto and Roboto Mono look better than Go and Go Mono and are the default on Android, ChromeOS, and other Google products. Noto Sans supports many more characters than default fonts and will help resolve issues like goki/gi#484 and goki/girl#2. The one thing that needs to be figured out is a way to optimize and only embed the Noto fonts that are needed, as all of them for every script would take a lot of space.