change doctype to html

[jronallo]

Would it be possible to update the doctype to HTML5? Right now the output is XHTML, which means that my pages do not validate since they use some of the new elements.

[alexch]

This is only tough because I think it requires a patch to Erector. Which isn't really that tough, but I haven't been inside the Erector codebase in a while and have been busy with other things...