Add support for [attr~="value"] selector (attribute contains word)

Add support for [attr~="value"] selector (attribute contains word)

http://www.w3.org/TR/CSS2/selector.html#attribute-selectors
http://api.jquery.com/attribute-contains-word-selector/

  This selector matches the test string against each word in the
  attribute value, where a "word" is defined as a string delimited by
  whitespace.  The selector matches if the test string is exactly equal
  to any of the words.