chat.api 0.1.0

• First CRAN release.
• A common interface for polling, sending, editing, reactions, attachments, room membership, history, state, and identity, with capability flags for adapter-specific support.
• An in-memory loopback adapter for local development and testing, plus adapters for Matrix, IRC, Slack, and Telegram.
• Matrix supports encrypted messaging, durable room-key requests, verification against local cross-signing keys, and credential persistence through mx.client and mx.crypto.
• Slack supports channel creation and leaving, bot identity customization, and posting as a workspace member when configured with a user token.
• Telegram supports long polling, threads, replies, files, edits, reactions, and identity. Requests can use httr directly or a telegram::TGBot object with its configured proxy.