Removed stop, transformed computations to be dynamic expr, sync extraction
Evaluation programs in the new semantics

Evaluation programs:
- Kpn: a Kahn process network of 6 nodes, generating all numbers of the
form 2^a * 3^b * 5^c. Currently contains much debug printing.
- Eratosthenes: implements the sieve as a process network. Every new
prime gets a new filter process
- Consort: concurrent sort an arbitrary int list spawning roughly n^2/2
processes that do swaps.

- Mvars: the examples use message variables. I have implemented them
with fifo queues: put is non-blocking always, take is blocking only when
the queue is empty.