bump up version to 0.5.7

bump up version to 0.5.6

bump up version to 0.5.5

bump up version to 0.5.4

bump up version to 0.5.3

Merge pull request #200 from motemen/bump-version-0.5.2

bump up version to 0.5.2

Merge pull request #195 from motemen/bump-version-0.5.1

bump up version to 0.5.1

Merge pull request #168 from motemen/bump-version-0.5.0

bump up version to 0.5.0

Merge pull request #148 from motemen/bump-version-0.4.1

bump up version to 0.4.1

Merge pull request #136 from motemen/bump-version-0.4.0

Bump up version to 0.4.0