added a test for HtmlElement.urlencode(). It works only under ruby 1.8
refactoring of HtmlElement.urlencode(). it can be used also in Ruby versions higher than 1.9.*
added more assertions to test_urlencode()
removed "o" option of the regular expression in HtmlElement.escape(),
as in this case, the encoding of the regular expression should automatically be US-ASCII in Ruby versions higher than 1.9.*
added a test for HtmlElement.urldecode()
refactoring of HtmlElement.urldecode(). it can be used also in Ruby versions higher than 1.9.*