Fix #117: Treat section as a block-level tag.

Here's my attempt to fix the issue. Added a spec to boot. Let me know what you think. I suspect other elements need to become similarly block-level too. Here's a list of HTML 5 block-level elements: http://www.whatwg.org/specs/web-apps/2007-10-26/multipage/section-documents0.html#block-level0