Allow more flexible control over the number of threads #23
Description
The only way to request a specific number of threads in galois_executor is to pass it as an argument of its constructor. This requires applications to accept it as a CLI argument, or use a fixed number of threads. Many example applications choose the second route, making it impossible to test their scalability.
It should be possible to set the number of threads using an environment variable, e.g. ADS_NUM_THREADS.