Combiner & BiFunction

[Brian Goetz]

> Can you also normalize the Function and Operator types name ?
>
> when it was Mapper instead of Function, it was not a big deal, but now
> with the name Function, Operator and Function names are not aligned.
>
>    Function -> UnaryOperator
>    BiFunction -> BinaryOperator

We discussed this one already and it seemed the conclusion was that 
people were comfortable with the assymmetry in order to get the benefit 
of not mucking up the most common type names?  The idea is that each 
base type (Function, Predicate, Block) had a "natural" arity and we'd 
only use the prefixes for other arities.