Develop

[waitxxxx]

New feature:

1. add eta time.
2. add flake8 code check.

Refactor:

1. init lmdb in init.
2. Avoid downloading data set files repeatedly.
3. save jpeg image to lmdb.
4. update scikit-image to 1.16.X

Fix:

1. warning of lr.step() before opt.stop().