Comp Expr start
Revert "Comp Expr start"

This reverts commit 21ee3f477540531dbde640a4fce147a00a8d99d3.
Comp Expr start
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.
Merge pull request #13 from tk407/CompExpr

Merge the new semantics in