Xmlm passes invalid characters into output

Character code 27 (ESC) passes unescaped into output XML. XML 1.0 requires absence of this and other control characters in its well-formedness criteria for documents. XML 1.1 allows this character with a numeric character reference.

Xmlm cannot consume ESC, emits ESC without escaping when found in `Data in XML 1.0 and XML 1.1 modes, and does not parse &#27; in XML 1.1 mode.