toRdf() and flatten() API require extractAllScripts to default to true

[gkellogg]

The JSON-LD section on JSON-LD in HTML Documents specifically says that all script all script elements are extracted, implying that the default value of |extractAllScripts| should be true for the toRdf() API entry point.

Tests for flatten() also say that it should extract all script elements, although there is no normative text to this effect.

Changing the behavior of flatten() would represent a change to the 1.1 behavior, but may be warranted.

The toRdf() entry point should be updated to say that the default is true.