don't make a close of time step functions
calculate dt_pre only once per time step
Merge pull request #34 from norihiro-w/fix-multiple-timestep-copy

Fix multiple timestep copy
Change back. The old setting was more appropriate.
Adding comments into the class. Also clean-up the format.
Merge pull request #24 from HaibingShao/Add_AdaptTimeSteping

Add adapt time steping