Expose Rust interfaces

[gi0baro]

As suggested by @sansyrox

Apart from producing wheels, building also a Rust library would be beneficial for projects like https://github.com/sansyrox/robyn

Exposing Rust APIs would let other Rust projects to take advantage of granian server interfaces to serve and interact with Python code.

This would probably require the re-design of server, protocols and types interfaces. A proper interface still need to be designed, probably starting from robyn needs.