Make example.html work again. Not the prettiest technique, but it works.

[RossPatterson]

Fixes #97.

I have a fix for this, but IMHO, it's ugly. The inability to run a <script type=module> synchronously with the page load makes it hard to get the railroad.js functions into a place where the diagram scripts can access them reliably. And the inability of an ES module script, even an inline one, to get document.currentScript, or to locate itself in the DOM, makes it hard to figure out where to insert the diagram SVGs.

My changes entail wrapping each <script> tag in a new <div>, and monkey-patching Diagram.addTo() to locate the appropriate <script> tag using a way that will work for example.html, even if it can't be generalized to other uses. Doing it this way buries the ugliness where nobody will see it when they're looking at the browser results (as opposed to the contents of the example.html file). Which is lame, but it works. Doing so results in examples that are coded like this:

<h1 id='ident'>IDENT</h1>
<div>
<script type=module>
ComplexDiagram(
	Choice(0, Skip(), '-'),
	Choice(0, NonTerminal('name-start char'), NonTerminal('escape')),
	ZeroOrMore(
		Choice(0, NonTerminal('name char'), NonTerminal('escape')))).addTo();
</script>
</div>