Implement HTMLUnknownElement::new.
Fix #1139: refactor return types in selector parsing code.
auto merge of #1138 : Ms2ger/servo/reflect-HTMLUnknownElement, r=jdm

@jdm: I think we should move nodes more in line with the rest of the DOM. How do you feel about something like this?
Implement insertBefore and reimplement appendChild.
auto merge of #1147 : SimonSapin/servo/refactor-selector-parsing, r=pcwalton
Fix some typos in error messages
auto merge of #1151 : guersam/servo/patch-1, r=metajack

Just a trivial fix.
Address review comments and replace add_to_doc with node_removed and node_inserted functions.
parallel selector matching
auto merge of #1136 : Ms2ger/servo/insertBefore, r=jdm
HTMLDirectoryElement should be 'dir'. Fix #1159
auto merge of #1160 : saneyuki/servo/dir, r=jdm

@Ms2ger?
Introduce HTML{Audio,Video}Element::new.
Introduce HTMLTable{Data,Header}CellElement::new.
Introduce HTMLHeadingElement::new.
Introduce HTMLIFrameElement::new.
Introduce HTMLImageElement::new.
Introduce HTMLUListElement::new.
Introduce HTMLTrackElement::new.
Introduce HTMLTableRowElement::new.