Extract DOM improvements into a MarkupImprover class
Improve the MarkupImprover class (hah!)

Code cleanup and a removal of XHTML-style xmlns on the <html> element.
Change to using HTML5 doctypes by default (fixes #24)
Use nested formatter when running rspec in guard
MarkupImprover: Reword and expand examples, document, refactor
AssetScanner should also strip HTML comments and CDATA