full rewrite for async/await

[museun]

This is the next version.

This is fully async/await and provides a feature to disable it.

When "async" isn't enabled, only messages encoding/decode/parsing and some helper utilities are available.

• InvalidMessage error implementation.
• Add a wait_for method
  • Connect should block until the CAPs are verified
  • Connect should block until 001 or 376 is received
    • on 001, return their username
    • on 376, return the twitch user
• More message / events types
  • 001 - irc ready
  • 376 - twitch ready
  • Error - an irc error
  • Notice - a lot of Twitch data is sent via noticed
  • ClearChat
  • ClearMsg
  • GlobalUserState
  • HostTargetEnd
  • HostTargetStart
  • Mode
  • ModeStatus
  • NamesEnd
  • NamesStart
  • MessageId
  • Reconnect
  • FollowersOnly
  • RoomState
  • NoticeType
  • SubPlan
  • UserNotice
  • UserState
• Channel type wrapper
• User type
  • Tags::get_user -> Option
• Optional serde integration
  • Determine what types should have derives
  • Feature-gate the derives
• Event ids for specific removal
• More methods on writer
  • ban :: username reason
  • clear
  • color :: color
  • command :: data
  • commercial :: length
  • delete
  • disconnect
  • emoteonly
  • emoteonlyoff
  • followers :: duration
  • followersoff
  • help
  • host :: channel
  • marker :: comment
  • me :: channel message
  • mod :: username
  • give_mod :: username
  • mods
  • op :: username
  • r9kbeta
  • r9kbetaoff
  • raid :: channel
  • raw :: data
  • send :: channel message # alias for privmsg
  • slow :: duration
  • slowoff
  • subscribers
  • subscribersoff
  • timeout :: username duration reason
  • unban :: username
  • unhost
  • unmod :: username
  • unraid
  • untimeout :: username
  • unvip :: username
  • vip :: username
  • vips
  • whisper :: username message
• More unit tests
• Note the MSRV (Minimal supported rust version)
  • Decide on a version, currently 1.40 is required for #[non_exhaustive]
• Fix github actions to use MSRV
  • Run rustfmt
  • Run clippy
• Add tokio codecs
  • Encoder
  • Decoder
• More logging
• Documentation
  • Ensure 'features' show up in the docs.
  • Many of the doc links are broken
  • Ensure the event -> message mapping table is up to date
    • Move this table out to a more prominent place
• Examples