javadoc improvements:
* diagrams for skip(t), single(), take(t), skipLast(t)
* minor corrections, reformatting of javadoc comments
Merge remote-tracking branch 'origin/master' into docs
Adding diagrams, improving javadocs for sumFoo/averageFoo operators.
Merge remote-tracking branch 'origin/master' into docs
adding diagram to repeat() javadocs
Merge pull request #700 from Netflix/docs

various javadoc improvements