code: function(years) {
  			years = years.split('.');
  			if (years.length < 3) {
  				throw 'Invalid Mayan year';
  			}
  			var year = 0;
  			for (var i = 0; i < years.length; i++) {
  				var y = parseInt(years[i], 10);
  				if (Math.abs(y) > 19 || (i > 0 && y < 0)) {
  					throw 'Invalid Mayan year';
  				}
  				year = year * 20 + y;
  			}
  			return year;
  		}
docs: Convert from the formatted year back to a single number.
  @memberof MayanCalendar
  @param years {string} The year as n.n.n.
  @return {number} The sequential year.
  @throws Error if an invalid value is supplied.