v5.0

What's Changed

• Add EventHandler by @nanato12 in #18
• Fix EventHandler and Dispatcher by @nanato12 in #19
• Add CommandHandler by @nanato12 in #20
• コマンドの引数を受け取るか判定する関数を実装 by @nanato12 in #21
• Refactoring and improvements by @nanato12 in #23

Full Changelog: v4.0.1...v5.0