v1.1.3.pre0

This prerelsease is for testing only. It's silly to release prereleases of patch releases, but I want to make absolutely sure that the optimizations in this release are correct.

• Optimizations in Future: no locks are taken once a future is completed (resolved/failed).
• Change from Mutex#synchronize to #lock/#unlock in most places. This might sound like a premature optimization, but these locks are in very hot paths and avoiding the yield in #synchronize decreases the overhead of around 40%.