Allow dynamic response generator for timeouts

There are cases where we are supposed to respond back with custom
information in the response in the event of timeouts. On the other
hand we  don't want to construct the response object unless it's
actually required. This change allows us to defer response creation
until we know it is required.
[maven-release-plugin] prepare release 0.96
[maven-release-plugin] prepare for next development iteration
Add REST endpoint to get MBean attribute value
Add AsyncSemaphore concurrent library
Add MBean attribute value REST endpoint release notes
[maven-release-plugin] prepare release 0.97
[maven-release-plugin] prepare for next development iteration
Make HyperLogLog.addHash public
Expose JettyHttpClient dump methods to JMX
[maven-release-plugin] prepare release 0.98
[maven-release-plugin] prepare for next development iteration