Agora RTC Objective-C API Reference Refactor

### - w -

- WatermarkBuffer() : WatermarkBuffer
- WatermarkConfig() : WatermarkConfig
- WatermarkLiteral() : WatermarkLiteral
- WatermarkOptions() : WatermarkOptions
- WatermarkRatio() : WatermarkRatio
- WatermarkTimestamp() : WatermarkTimestamp
- whereNow:completion: : AgoraRtmPresence
- whoNow:channelType:options:completion: : AgoraRtmPresence
- writeLog() : ILogWriter , IRtcEngine
- writeLog:content: : AgoraRtcEngineKit