Initiative: Expand character set

Creating this issue to gather all context and info about our initiative to expand the character set. A few issues have been created already:

**Latin**
- https://github.com/github/mona-sans/issues/8
- https://github.com/github/mona-sans/issues/17
- https://github.com/github/mona-sans/issues/28

**Ligatures**
- https://github.com/github/mona-sans/issues/23

Leaving all of these issues open for now, since they are slightly different and contain valuable context. Feedback is welcome both in this issue and in those separate issues, as we define the scope for expanding the character set.