Fix JavaDoc to enable build on Java 8

I fixed errors reported by doclint to allow project to build on Java 8 which is better than [turning doclint off](http://blog.joda.org/2014/02/turning-off-doclint-in-jdk-8-javadoc.html). Still there are 65 warnings that should be resovled. Most of them are `no description for @param`.