Code format tidying.

* Use upper-case for all tag names.
* Tidy document reference.
Add support for defaultBlockProperties.

Set the defaultBlockProperties property on a squire instance to an object and
it will use these properties when it has to create a new default block element.
Ensure there is always a normal block at the bottom of the page.
Don't change encoding of URL in Squire#makeLink.

Presume the URL is already valid, otherwise we could end up double encoding.