Add line breaks for readability.
Rename the element field of the DOM Node hierarchy.

See #924
Auto-generate some binding codes for HTMLElement, Element, CharacterData.
auto merge of #1064 : saneyuki/servo/cleanup, r=jdm

This pull request is based on #1063.
Added configuration binding.
Added Main element
WebIDL definition of MainElement
Added HTMLMainElement
Added HTMLMainElementTypeId
Added main element to parser
Added htmlmainelement implementation
added htmlmainelement
Added test for HTMLMainElement
fixed merge conflict