Splitio-client

- Bumped mmh3cffi dependency which now requires c99 flag to build.

- Added RecordStats for supporting pipelined recording in redis when treatment call is made.
- Added hooks support for preforked servers.

- Fixed error handling when split server fails, so that it doesn't bring streaming down.
- Added SDK Metadata headers to split & segments API clients

- Added local impressions deduping. Defaulting to optimized
- Added support for the new Split streaming architecture. When enabled (default), the SDK will not poll for updates but instead receive notifications every time there's a change in your environments, allowing to process those much quicker. If disabled or in the event of an issue, the SDK will fallback to the known polling mechanism to provide a seamless experience.
- Updated logging structure so that it's built in terms of a hierarchy with the root at 'splitio'
- Fixed timing issue which caused factory.ready to return False if called immediately after .block_until_ready()

- Updated mmh3cffi to version 0.1.5 which fixes xcode12 issue

- Added support for enabling in-memory cache via config options