Merge pull request #10 from MaxMEllon/develop

merge: develop -> master
Added Gitter badge
Merge pull request #11 from gitter-badger/gitter-badge

Add a Gitter chat badge to README.md
Merge pull request #13 from MaxMEllon/fix

Fix
Merge pull request #15 from MaxMEllon/develop

merge: develop -> master
Merge pull request #16 from MaxMEllon/develop

merge: develop -> master
feature: 人対人の対戦を可能に
fix: () -> と ()-> が混ざっていたのを ()-> に統一