Move KNoT protocol specific code to one package

[esdrasjnr]

In order to modularize babeltower code and makes KNoT protocol changes easily, it would be nice to have an package for KNoT protocol methods and constants.

[ramonhpr]

Hello everyone! I have a proposal about that.
I've made a PoC using protocol buffer (https://developers.google.com/protocol-buffers) in knot-protocol-source. So we don't need to duplicate code related to headers in C on knot-protocol, avoiding the need to replicate changes made on protocol in each different language that we use like Javascript and Go.
Instead we clone the repository and build to the desired programming language that we want. I've made tests using C and python. And Golang is supported for protobuff!
Remembering that the babeltower doesn't need to serialize the messages on protocolbuffer but only use the structs that will be genereated.

The PoC can be found on here: https://github.com/ramonhpr/knot-protocol-source/tree/protobuff
And it depends on protocol buffer and libprotobuff-c (that last can be made optional depending on the desired programming language)
To install it use: ./bootstrap-configure --enable-protobuff

What do you think @netoax @vitbaq @alla3 ?