Remove or fully specify the <image> element

[prushforth]

I note that there is still an image element, although it's not really specified properly. I think we should remove it until we're ready to design it a little bit more. Probably don't want another image element in HTML anyway TBD.

[Malvoz]

There are related comments in #70 that are worth mentioning:

• image: the HTML parser treats <image> as a macro and changes it to <img>. New element name?

Maybe img? Map images aren't that different from regular images, and instead of extending the set of elements we apply the same re-use of existing semantics but update the rendering model?

It may be better to have a new name as to not be confused with the <img usemap=""> element (#217).