Merge pull request optuna#298 from pfnet/bump-to-v0.6.0

Bump up version number to 0.6.0

Merge pull request optuna#271 from pfnet/v0.5.0

Bump up version number to 0.5.0

Merge pull request optuna#247 from pfnet/iwiwi-patch-1

Add `url` information to `setup.py`

Merge pull request optuna#183 from pfnet/update-version-0.3.0

Update the version to 0.3.0.

Merge pull request optuna#165 from pfnet/update-ver-0.2.1

Update version to 0.2.1

Merge pull request optuna#159 from pfnet/version-0.2.0

Update version to 0.2.0.

Merge pull request optuna#120 from pfnet/update-version-0.1.0

Update version to 0.1.0