crossbeam 0.2.5

Support for lock-free data structures, synchronizers, and parallel programming
# Version 0.2

- Changed existing non-blocking `pop` methods to `try_pop`
- Added blocking `pop` support to Michael-Scott queue
- Added Chase-Lev work-stealing deque

# Version 0.1

- Added [epoch-based memory management]http://aturon.github.io/blog/2015/08/27/epoch/
- Added Michael-Scott queue
- Added Segmented array queue