///|
/// HTML escape a string
fn html_escape(s : String) -> String {
  let buf = StringBuilder::new()
  for char in s {
    match char {
      '<' => buf.write_string("<")
      '>' => buf.write_string(">")
      '&' => buf.write_string("&")
      '"' => buf.write_string(""")
      '\'' => buf.write_string("'")
      _ => buf.write_char(char)
    }
  }
  buf.to_string()
}