v0.0.1 of dart_plex

Dart client for Plex Media Server. Supports authentication, library browsing, playlists, audio streaming, lyrics, playback reporting, search and more. Targets macOS, Windows, Linux, iOS and Android. Changelog excerpt: ### Added - Initial scaffold targeting Plex Media Server v1.43.x. - Authentication flows: legacy username/password and the official PIN link. - PMS HTTP client with X-Plex-*header injection (client identifier, product, version, device, platform, token). - Exception hierarchy with semantic error classification (auth, notFound, serverError, parse, state, connection, timeout, badRequest, unknown). - Music endpoints: libraries, sections, items by type, playlists, artwork, audi[...]