version should have  -SNAPSHOT
[maven-release-plugin] prepare release jpush-client-2.3.0
[maven-release-plugin] prepare for next development iteration
[maven-release-plugin] prepare release jpush-client-2.3.1
[maven-release-plugin] prepare for next development iteration
Change to log4j as default logging library.
Add libs/ for non-maven usage.
Update README.md
Update README.md