* Fix color support for stretchy, strikethrough, and fbox
Summary:
Stuff like `\red{\overbrace{AB}}` works now in addition to `\color{red}{\overbrace{AB}}`. Strikethrough now respects color. The Firefox in the screenshotter doesn't seem to support `background-image` + `mask`, but I manually tested that the latest Firefox does.
Test plan:
Ran `make`, then tested in latest Chrome and Firefox to ensure color support was working, then ran `make screenshots`.
* Add a maxSize option to limit user-specified sizes (#109)
* Simplify maxSize logic and add unit test
* Clamp negative maxSize to zero
* Use a default maxSize of infinity to remove branching in calculateSize
