Misc fixes

[dpvc]

This is a collection of miscellaneous fixes that I have accumulated while updating the documentation for v4.

The makeAll and pack changes are to handle building of fonts and third-party extensions better.

The assistive-mml change is to prevent the assistive MathML representation from being pushed outside the bounding box of the MathJax output.

The lite/Element.ts changes are to prevent the version mismatch error when a node application uses MathJax components rather than direct calls, and the loader uses the MathJax.loader.load() command.

The components/package.ts change is to get the proper result returned when require() is used in MathJax.loader.load (e.g., when MathJax = {loader: {require: require}} is used in CommonJS applications).

The components/startup.ts change is to add a MathJax.whenReady() command to access the document's whenReady() method.

The RequireConfiguration.ts change is to prevent an error when the menu code isn't loaded (e.g., when components are loaded by hand rather than through a combined component, and ui/menu isn't included).

The mmultiscripts.ts change is to avoid a bug in WebKit that causes incorrect placement of scripts when <none> is used as a superscript in <mmultiscripts>.