Evovle the pool from locked counters to atomic counters
Evovle the pool from locked counters to atomic counters

 - choose geeky numbers for tests
 - Add a new Test for massive task creation
 - Add new test for shrinking the pool
 - Let the test wait with a barrier not with a machine dependant sleep.

rust-threadpool/rust-threadpool,frewsxcv/rust-threadpool,rust-lang/threadpool