Merge pull request #14 from otiai10/develop

Remove unnecessary file
Merge pull request #15 from otiai10/develop

Refactor
Merge pull request #16 from otiai10/develop

Add badge
Merge pull request #17 from otiai10/develop

develop
Merge pull request #21 from otiai10/develop

Develop
`Group` to `ScoredSet` #22
`Element` to `ScoredValue` #22