Merge pull request #51 from allenxwang/cp

Add async HTTP support based on Apache's HttpAsyncClient
Merge pull request #54 from allenxwang/cp

Upgrade httpasyncclient version to 4.0 GA. Added concurrency and read timeout tests.
[Gradle Release Plugin] - new version commit:  '0.3.1'.
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Merge pull request #56 from allenxwang/cp

Fix RestClient connection leaks when it throws ClientException upon server throttle. Enhanced JUnit tests for RestClient retries.
[Gradle Release Plugin] - new version commit:  '0.3.2'.
Update CHANGES.md
Make sure NamedConnectionPool instances register with Servo with unique names.