Add Travis CI configuration file
Add a profile to enable gpg signing only for releases.

Update travis configuration file, -Dgpg.skip=true no longer required.
Travis CI does not provide oraclejdk6

"Travis CI provides OpenJDK 6, OpenJDK 7 and Oracle JDK 7. Sun JDK 6 is not provided and because it is EOL as of November 2012."
Update mvn profile to enable gpg signing on demand.

Use "mvn -Pgpg" to enable gpg for a specific build. By default gpg is disabled.
Merge pull request #41 from cykl/travis-ci

Enable Travis CI