Minor updates to IVar API.
Initial spike of Concurrent::Async
Wrote YARD doc for Async module.
Added specs for Async::validate_argc
Full specs for Async module (with a few pending.
Fixed metaprogramming bug in Concurrent::Async
Better mutex handling in Async mixin.
Better tests for Async mixin.
Merge pull request #37 from jdantonio/async-await

Async and Await