Build separate vertical and horizontal modules

This allows separate imports for vertical and horizontal libraries, and gives a way to import the library outside of webpack.

webpack.config.js

@@ -0,0 +1,13 @@
+var path = require('path');
+module.exports = {
+  entry: {
+    horizontal: './shim/horizontal.js',
+    vertical: './shim/vertical.js'
+  },
+  output: {
+    library: 'ScratchBlocks',
+    libraryTarget: 'commonjs2',
+    path: path.resolve(__dirname, 'dist'),
+    filename: '[name].js'
+  }
+};