Release v4.0.0-rc.1

What's Changed

• Split status manager from client by @huangdijia in #2
• Optimize by @huangdijia in #4
• Fix the bug that not run keepalive by @huangdijia in #6
• Fix the bug that set offline do not remove from set by @huangdijia in #8
• Optimize auto cleanup expired clients by @huangdijia in #9
• Adds SubscriberFactory by @huangdijia in #11

Full Changelog: v3.1.1...v4.0.0-rc.1