Add support for Latin-1, Cyrillic, and CJK characters inside \text{} (#508)

Summary:
This diff provides support for Latin-1, Cyrillic, and CJK characters
inside \text{} groups.  For Latin-1 and Cyrillic characters we use
glyph metrics from a glyph from Basic Latin that has roughly the same
bounding box.  We use the metrics for a capital 'M' to approximate the
full-width CJK characters.  Half-width characters are not supported yet.

Test Plan:
- make test
- make screenshots

Reviewers: emily

.gitignore

@@ -9,3 +9,4 @@ diff.png
 /test/symgroups.aux
 /test/symgroups.log
 /test/symgroups.pdf
+/test/screenshotter/unicode-fonts