/**
 * Returns the substring between two strings, delimiters not included
 * @param string $string Haystack
 * @param string $start Starting delimiter
 * @param string|null $end Ending delimiter, if omitted will return the rest of the string
 * @return bool|string The substring between $start and $end or false if either string is not found
 */
function substr_between($string, $start, $end=null) {
	if(($start_pos = strpos($string, $start)) !== false) {
		if($end) {
			if(($end_pos = strpos($string, $end, $start_pos + strlen($start))) !== false) {
				return substr($string, $start_pos + strlen($start), $end_pos - ($start_pos + strlen($start)));
			}
		} else {
			return substr($string, $start_pos);
		}
	}
	return false;
}