fix(lib): Expose commitizen as a library

This fixes index.js so that it exposes commitizen as a library.

Closes #80

src/index.js

@@ -1,17 +1,2 @@
-function all() {
-  console.log('all');
-}
-
-function random() {
-  console.log('random');
-}
-
-function randomItems() {
-  console.log('randomItems');
-}
-
-module.exports = {
-  all:all,
-  random:random,
-  randomItems:randomItems
-};
+var commitizen = require('./commitizen');
+module.exports = commitizen;