Refactored DefaultHtmlElementFinder and HtmlElementFinderBase to support flexible XPath axes.
Added AncestorHtmlElementFinder.
Added FindAncestor<T>() to IHtmlPage and HtmlElement.
Updated GetHtmlForm to use FindAncestor.
Refactored GetHtmlForm extension to be HtmlFormElement.Form.
Refactored table support from methods to properties on rows and cells.
Closes #3.