Update VOICEVOX character list and docs (#19)

feat: Enhance URL extraction and text management features

Fix spelling of "YomiTalk" to "Yomitalk" in code and documentation for consistency

テキストファイル形式のサポートを追加

PyMuPDF (fitz) の依存関係を削除し、VOICEVOXの初期化処理を改善

Initial commit: Set up YomiTalk project