Merge pull request #100 from ruby-concurrency/actress

Actress post release fixes
Released 0.6.1
Fixed doc entry mistakenly removed from .gitignore.
Removed old Actor.
Removed deprecated Runnable methods from TimerTask.
Removed Stoppable, which is no longer being used.
Removed Runnable, which is no longer being used.
Added [EXPERIMENTAL] warning to Supervisor.
Merge pull request #112 from ruby-concurrency/remove-old-actor

Remove old Actor
wip: Initial import of ruby-atomic.
Fixed broken Java build.
Added legacy Atomic class with deprecation warning.
Triggering TravisCI build of atomic-reference branch.
Specs with native extensions passing on MRI, JRuby, and Rubinius.

Added fake_build hook back to extconf.rb
Atomic specs now defined by share_examples_for

wip: Updated atomic_spec to support platform-specific testing.
Atomic now extends platform-specific implementation; defaults to MutexAtomic.
Updated atomic benchmarks to test all available implementations.
Updated build tasks to support rake-compiler-dev-box

wip: Updates to suppoer rake-compiler-dev-box
First successful gem build using custom rake-compiler-dev-box.

Removed superflouous lines from gemsepc and Rakefile.

Fixed CAtomic load error for Windows cross-compiled extensions.
Gems built with new build boxes and tested no several operating systems.

C extensions added back to platform-independent gem.

Fixed platform-independent gem build.

Platform-independent build now works the way we intend.

Fixed package and build problems in Rakefile.

Better error messages.

Reduced the number of threads in atomic parallel tests.