Checkbox `defaultChecked` not working

It seems the property for starting the box checked, and allowing user to change it doesn't work. If 'checked' property is used, it doesn't allow user to change it (unlike HTML input checked prop), and the `defaultChecked` doesn't start the box checked.

Using version 0.1.1 with React 16.4.1

No file, test, or entry point is named. Start by reproducing the Checkbox behavior described against version 0.1.1 and trace the component implementation and its existing tests. Done means the initial checked state works with defaultChecked while users can change it, and checked behavior matches the reported HTML input expectation.

Written by the indexing model from the issue text.