Emitter-io

This release removes private links (normal links are still there) and introduces a way of creating private keys by simply calling `keygen` with an "extendable" key (ie. a key with `e` permission). On top of that, it has a few optimisations and emitter now defaults to using/generating license v2 which was introduced a few months ago.

Changelog
- Added chunking before sending through to the gossi unicast, given that the max frame is 10MB we can send at once (254)
- Added a debug mode flag in the config. Ppprof HTTP endpoints are now by default disabled and you'll need to flip the flag on to enable them (255)
- Fixed a security issue by disallowing pub/sub on extended keys (262) (261)
- Added a way to extend keys through a normal keygen method. Users will need to provide a key which has extend permissions in the request along with the desired access permissions. Note that the permissions will be a reflection of the key itself (e.g: if a key has re permissions and keygen request contains wr, the resulting key will only have r permission) (268)
- Upgraded the dependencies and made v2 license default. (278)
- Removed private links as they have been replaced with a keygen. This is to make sure there's only one way of extending keys and keep the API relatively simple to understand. (279)

This release makes flush and read rate limiting configurable which allows brokers to be more protected against misbehaving clients.

Change Log:

- Made flush rate configurable for tuning socket writes (250)
- Removed 1 alloc in channel validation (251)
- Added a read rate limiter which allows limiting the read QpS per client (252)

Allows setting a username when connecting, which is important for Presence.

Added and documented the new keyban API.

Private links no longer exist. One can create a private channel using the keygen command with an extendable channel.