Make sure these boxes checked before submitting your pull request.
- [] Do only one thing
- [] No API-breaking changes
- [] New code/logic commented & tested
- [] Write good commit message, try to squash your commits into a single one
- [] Run `./build.sh` in `gh-pages` branch for document changes
For significant changes like big bug fixes, new features, please open an issue to make a agreement on an implementation design/plan first before starting it.
