String.startsWith()

Pushes support back to at least IE6.

/**
 * String.prototype.startsWith() polyfill
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith#Polyfill
 */
if (!String.prototype.startsWith) {
	String.prototype.startsWith = function(searchString, position){
		return this.substr(position || 0, searchString.length) === searchString;
	};
}