Added a new class ShutdownListener which listens for ApplicationContext closed events and shuts-down Ektorp.
Added additional documentation to the ShutdownListener.
Merge pull request #179 from dlvenable/spring_shutdown_listener

Spring shutdown listener
changelog for 1.4.2
[maven-release-plugin] prepare release org.ektorp.parent-1.4.2
[maven-release-plugin] prepare for next development iteration
using a ThreadLocal in order to maintain 1 instance of ObjectMapper per Thread, instead of 1 instance for the whole StdCouchDbConnector. This greatly reduces contention on ObjectMapper internal state synchronization when multiple thread are using it at the same time, which is often the case in a server side application.
in case of an update conflict, the response content should be consumed, in order to comply with HttpClient usage best practice for using keep alive