Remove actor-experimental warning.
Create an IndirectImmediateExecutor
Implement IndirectImmediateExecutor with just one PerThreadExecutor
Add specs for IndirectImmediateExecutor characteristics
Merge pull request #165 from ruby-concurrency/actress

Remove actor-experimental warning.
Allow to disable auto termination of global executors

It was causing trouble when the gem was used in test-suites of other projects.
Merge pull request #167 from pitr-ch/pools

Allow to disable auto termination of global executors
Merge pull request #166 from obrok/indirect-immediate-executor

Create an IndirectImmediateExecutor