add basic saving feature to local. fixes #16

src/utils.js

@@ -0,0 +1,36 @@
+// https://github.com/substack/semver-compare/blob/master/index.js
+function semverCompare(a, b) {
+	var pa = a.split('.');
+	var pb = b.split('.');
+	for (var i = 0; i < 3; i++) {
+		var na = Number(pa[i]);
+		var nb = Number(pb[i]);
+		if (na > nb) { return 1; }
+		if (nb > na) { return -1; }
+		if (!isNaN(na) && isNaN(nb)) { return 1; }
+		if (isNaN(na) && !isNaN(nb)) { return -1; }
+	}
+	return 0;
+}
+
+function generateRandomId(length) {
+	length = length || 10;
+	var id = '';
+	for (var i = length; i--;) {
+		id += String.fromCharCode(~~(Math.random() * 52) + 65);
+	}
+	return id;
+}
+
+function onButtonClick(btn, listener) {
+	btn.addEventListener('click', function buttonClickListener() {
+		listener();
+		return false;
+	});
+}
+
+function log() {
+	if (window.DEBUG) {
+		console.log.apply(console, [].splice.call(arguments, 0));
+	}
+}