Support template script tags

Not 100% sure about this. This will include HTML highlighting in script tags with the following types: `text/html` `text/x-handlebars` `text/x-handlebars-template` `text/template`. Those are the most common types that I know.

There's an issue in that if you use these in say, a PHP file, PHP will not be highlighted within the tags. Is there a way to include the parent scope instead?