Module pattern is now implemented via templating

Previously two modules were defined, Layout.js, which is the internal implementation, and main.js, which depended on Layout.js and performed the fill / extract functionality required for a public JavaScript API.

This simplifies the implementation by just exposing a single UMD module by directly including Layout.js within the module wrapper.

Fixes #103

src/css-layout.js

@@ -0,0 +1,25 @@
+// UMD (Universal Module Definition)
+// See https://github.com/umdjs/umd for reference
+(function (root, factory) {
+  if (typeof define === 'function' && define.amd) {
+    // AMD. Register as an anonymous module.
+    define([], factory);
+  } else if (typeof exports === 'object') {
+    // Node. Does not work with strict CommonJS, but
+    // only CommonJS-like environments that support module.exports,
+    // like Node.
+    module.exports = factory();
+  } else {
+    // Browser globals (root is window)
+    root.computeLayout = factory();
+  }
+}(this, function () {
+    // @@include('./Layout.js')
+
+    return function(node) {
+      node = computeLayout.fillNodes(node);
+      computeLayout.computeLayout(node);
+      node = computeLayout.extractNodes(node);
+      return node;
+  };
+}));