concurrency_traits 0.4.0

Traits for concurrent primitives.
Documentation
## concurrency_traits v0.4.0
- Added general system traits

### concurrency_traits v0.3.1
- Added `TimeoutQueue` and `AsyncTimeoutQueue`

## concurrency_traits v0.3.0
- Made `ThreadSpawner` able to handle errors

## concurrency_traits v0.2.0
- Added implementations for std lib and parking_lot
- Changed blanked `Deref` impls to targeted impls

# concurrency_traits v0.1.0
- Initial Version!