To @flow: fontMetrics, fontMetricsData, Options, Settings, Style (#848)

*     To @flow: fontMetrics, fontMetricsData, Options, Settings, Style

* Don't overuse $Shape, improve type checking for fontMetrics*, make maxSize required in OptionsData and update callers.

* Remove eslintrc globals change, since eslint-plugin-flowtype makes it redundant.

* Remove extra ?s in Options and Settings

* Undo removal of width in fontMetrics and switch to `T | void` for nullable types in Options

* fix typing of FontMetrics

test/mathml-spec.js

@@ -21,6 +21,7 @@ const getMathML = function(expr, settings) {
     // Setup the default options
     const options = new Options({
         style: startStyle,
+        maxSize: Infinity,
     });
 
     const built = buildMathML(parseTree(expr, usedSettings), expr, options);