"hydra" support

[SunQpark]

Hydra is a python package for handling config files developed by facebook research team.
Recently I noticed that using this package can simplify source code of this project a lot, by replacing following features with package functions.

• using CLI options to change config
• object initialization from config
• accessing config items as attributes (using config.something, instead of config['something'])
• managing checkpoint directory with timestamp

Since replacing current implementations with a package can be seen as a quite radical change, I made separate hydra branch to use this package. Comparing with master branch, this version will

• have much simpler design
• contain some advanced features
• be maintained more frequently (since I'm not using master version any more)
• contain some bugs yet...

If you are interested, checkout to that branch by git checkout hydra on this repository