Threads: handles request with threads

Threads: handles request with threads

This implementation handles all requests with threads.
Later implementation could add a mechanism to choose
what request will be handled by threads.

Each API receive its requests in serial order without
reentrancy. Here again, this can change in the future
if a choice is possible to allow reentrant calls.

The signal/event are not processed using threads
in this version. It may change in the future.

Signed-off-by: José Bollo <jose.bollo@iot.bzh>