Refs #323. Added a test demonstrating the parser bug.

I hate you, parser.
Added a few test cases showing bug
Added a new xhtml parser mode to handle self closing tags
Self closing tags that are not valid inline_tags trigger ClosingTag method
Added a new test for iframes and reworked embedded tests to be treated as void tags
Reworked selfclosing tag behaviour and added iframe to block tags list
Merge pull request #382 from craigerm/selfclosingtag-mode

Fixes #323. Added SelfClosingTag mode to support inline tags