Fixing default chunk sizes (greatly improved performance).

If the chunk size is not specified, using the default size of one leads to no parallelization in most cases. The queue size should be >= the number of workers and it can help to "prefill" it with extra elements.

Fixes

1. Fixing the bugs (not immediate shutdown in the case of exceptions, and not updating the bar properly) for unbounded mode.
2. Deprecating task timeouts.

v0.2.1

This release fixes several documentation issues and removes a debug statement from a unittest module.