HTML in slide titles is inserted into skip links

[smhigley]

If I have a slide title like this:
Something about a <code>&lt;button&gt;</code>

Rendered on the slide as:
Something about a <button>

it causes an actual <button> element to be inserted into the skip link for that slide, since the skip link html is constructed by appending the return value from .textContent directly to an html string.