Operations Aggregate, Average and Sum with selector
Merge branch 'AggregatorsWithSelector' of github.com:akarnokd/RxJava into pull-657-merge
Remove newly added aggregate methods

- avoiding methods with `index`
- resultSelector overload is same as `reduce(seed, accumulator).map(resultSelector)`
Rename to ReduceTest
Merge pull request #698 from benjchristensen/pull-657-merge

Merge of Pull 657: Average and Sum
Merge remote-tracking branch 'origin/master' into docs
Adding diagrams, improving javadocs for sumFoo/averageFoo operators.