Fix a bug that removing multiple layer of <div>s at once would cause error. Unit test added.
Fix a bug that _seess_diff_id_ on body would not be marked. The walker was not set up correctly and skip the root (<body>)
MERGE
Add `gulp` in README
Use window.parent.chrome.runtime to perform quick test because
window.parent.location.origin triggers SecurityError
Site under test
Depress unnecessary return
Fix a bug that testing detection throws exception when there is no <script> in document
Prioritize rendererScript’s loading order so that renderer can postMessage to rendererScript