Adds maven-release-plugin

Automates the following steps:
* Increment version and produce release build
* Commit changes and push to master branch on GitHub
* Create tag and push to GitHub
* Deploy to Sonatype Nexus

Usage
```
$ mvn release:prepare -DignoreSnapshots=true
$ mvn release:perform
```

**Requires Sonatype credentials to be added to local `.m2/settings.xml`.**

http://maven.apache.org/maven-release/maven-release-plugin/index.html