/*
 * call-seq:
 *   easy.unescape("some%20text")                     => "some text"
 *
 * Convert the given URL encoded input string to a "plain string" and return
 * the result. All input characters that are URL encoded (%XX where XX is a
 * two-digit hexadecimal number) are converted to their binary versions.
 */
static VALUE ruby_curl_easy_unescape(VALUE self, VALUE str) {