Implement Cyclic Learning Rate and Step-wise Learning Rate Scheduler

[Franklalalala]

As mentioned in [issue 211], this PR aims to Implement Cyclic Learning Rate and Step-wise Learning Rate Scheduler.

Major changes include:

1. add a Cyclic Learning Rate in tool.py and corresponding args.
2. add step-wise lr update scheme in trainer.py and base_trainer.py.
3. unit test, here I implemented 4 cases, which are mesh test on two lr scheme, exp and clr, and w/wo iteration-wise lr update

Minor change:

1. docs have been updated in argcheck.py
2. use the 'display_freq' as the tensorboard log interval (per-iteration), instead of using a fixed 25 iteration interval.

[Franklalalala]

The code has been cleaned. It is now the same with the upstream.

[Franklalalala]

the test example has been updated:
the dataset size was reduced from 5MB to 68KB