Add a maxSize option to limit user-specified sizes (#803)

* 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

test/katex-spec.js

@@ -2308,3 +2308,25 @@ describe("Unicode", function() {
         expect("ΓΔΘΞΠΣΦΨΩ").toParse();
     });
 });
+
+describe("The maxSize setting", function() {
+    const rule = "\\rule{999em}{999em}";
+
+    it("should clamp size when set", function() {
+        const built = getBuilt(rule, new Settings({maxSize: 5}))[0];
+        expect(built.style.borderRightWidth).toEqual("5em");
+        expect(built.style.borderTopWidth).toEqual("5em");
+    });
+
+    it("should not clamp size when not set", function() {
+        const built = getBuilt(rule)[0];
+        expect(built.style.borderRightWidth).toEqual("999em");
+        expect(built.style.borderTopWidth).toEqual("999em");
+    });
+
+    it("should make zero-width rules if a negative maxSize is passed", function() {
+        const built = getBuilt(rule, new Settings({maxSize: -5}))[0];
+        expect(built.style.borderRightWidth).toEqual("0em");
+        expect(built.style.borderTopWidth).toEqual("0em");
+    });
+});