Dynamically-controllable retrace (or "programmable retrace")

[ronaldtse]

As @ikolomi said,

I am almost done adding cli infrastructure to retrace, this will tranform retrace from passive to interractive interceptor - (user can initialize commands from a cli).

I remember @riataman was interested in a dynamically-driven retrace. Given the retrace framework we could take it one step further in making it programmable, so you can actually change how a binary works using a program as an "intelligent driver".

For example, the way we're using it for DNS queries is really primitive that needs a shell timeout command, pre-generation of retrace config files, parallel forking etc. This could all be done within a small driver program that links to retrace.

Thoughts?