Add WASM shim

[k82cn]

wasmtime is a WASM runtime, it's easy to integrate with high performance.

[k82cn]

Add service interface:

trait FlameService {
  on_service_create(ServiceContext);
  on_session_enter(SessionContext);
  on_task_invoke(TaskContext);
  on_session_leave();
  on_service_destroy();
}

Add WASM wrapper to get/set parameters of them, and the WASM should start with flame:run, for example:

struct MySvc {
};

impl FlameService for MySvc {
}

fn main() {
    let my_svc = xxx;
    ...
   flame::run(my_svc);
}

[k82cn]

fixed by #78 #77 #75