homepage

Here is an initial implementation. Differences from threading.Barrier:
- I have not implemented reset().
- wait() returns 0 or -1. One thread returns 0, the remainder return -1.
 This is different to threading.Barrier where each of the N threads 
 returns a unique index in range(N).
- I added an "action_args" parameter to the constructor. This is a tuple 
 which provides argument to the "action" callback. (This is because closures
 are not picklable, making no-argument callbacks rather limiting for 
 multiprocessing.)