Build optimization and updates

 - Update gradle to version 1.9
 - Enable 'parallel' and 'daemon' options for gradle
 - Have travis.ci build on both java6 and java7
Javadoc for ResizeEffect.
Relates to #25.
Merge pull request #28 from dougborg/gradleUpdates

Build optimization and updates
Remove slf4j.
Don't publish JavaDoc unless master was pushed.
Closes #30.
Only publish Javadoc with JDK7.
It's prettier that way :-)
More JavaDoc.
This closes #25.
Since there's a lot of work to be done with SquareButton and #20 (currently in progress), I'm going to leave that out for now.