* handle asp style tags in $php_handler
* correctly capture nested php tag syntax in templates:
  <?php echo "<?php exit(); ?>"; ?>
* support implementations of prefiltes, mods, and others as class methods.
* possibly implement default modifiers that apply to variables upon display
* think about possibility of supporting something like {$data[foo].$key[bar]}
* allow {custom} .. {/custom} style of custom functions
* ability to concatenate values/strings together
* fix all E_NOTICE warnings
* make simple math easier
* caching all but parts of the template