Refactor code to support building against Java 1.6
Add Java 6 testing to Travis setup
.travis.yml: remove 'oraclejdk6' because Travis does not support it anymore
pom.xml: automatically detect JDK major version (6/7) for builds
Update README with list of compatible Java versions.
Merge pull request #3 from miguno/travis

Support building against Java 6 and 7, including Travis testing