rvest 0.3.0

• rvest has been rewritten to take advantage of the new xml2 package. xml2
  provides a fresh binding to libxml2, avoiding many of the work-arounds
  previously needed for the XML package. Now rvest depends on the xml2
  package, so all the xml functions are available, and rvest adds a thin
  wrapper for html.
• A number of functions have change names. The old versions still work,
  but are deprecated and will be removed in rvest 0.4.0.
  • html_tag() -> html_name()
  • html() -> read_html()
• html_node() now throws an error if there are no matches, and a warning
  if there's more than one match. I think this should make it more likely to
  fail clearly when the structure of the page changes.
• xml_structure() has been moved to xml2. New html_structure() (also in
  xml2) highlights id and class attributes (#78).
• submit_form() now works with forms that use GET (#66).
• submit_request() (and hence submit_form()) is now case-insensitive,
  and so will find <input type=SUBMIT> as well as<input type="submit">.
• submit_request() (and hence submit_form()) recognizes forms with
  <input type="image"> as a valid form submission button per
  http://www.w3.org/TR/html-markup/input.image.html