Smarty-mode is for highlighting html templates written for the smarty
template engine (http://smarty.php.net).  This mode *does not* inherit
from html-mode since that mode seems like it might interfere with
what template designers might be trying to do.  This mode makes an
attempt to deliberately ignore html and highlight only smarty code.

Since this is my first go at writing a major mode, this is pretty basic,
and may very well contain bugs.