- metal to do macro expansion (default on)

- tal to do TAL expansion (default on)

- html for XHTML heuristics (default off).  See
  http://www.w3.org/TR/xhtml1/#guidelines for what this should do;
  currently all it does is to suppress the XML declaration and insert
  a space before the /> in minimized elements.

Changed the TALCompiler class to generate enough code to be able to
implement the tal=0 and metal=0 options to TALInterpreter; this meant
e.g. compiling the original contents of nodes subject to replacement.