More proper support for activities, fix small bugs

• Add rate limiting on activity update
• Add activity builder
• Fix bug with partial emojis being animated when they shouldn't

Presence & request guild members

• Properly handle websocket ratelimiting
• Add functionality to update presence
• Add functionality to request guild members

Full Changelog: 0.0.1...0.0.2

First release

• Connects to websocket
• Limited rest capabilities