Stream generators

[Brian Goetz]

We've got a few generators for infinite streams already implemented. 
For object streams:

   // produces seed, f(seed), f(f(seed)), ...
   <T> iterate(T seed, UnaryOperator<T> f)

   // infinite constant sequence
   <T> repeat(T t)

   // finite constant sequence
   <T> repeat(int n, T t)

   // infinite sequence driven by a supplier function
   <T> repeatedly(Supplier<T> f)

   // finite sequence driven by a supplier function
   <T> repeatedly(int n, Supplier<T> f)

   // infinitely cycle through an Iterable
   <T> cycle(Iterable<T> iterable)

For integer streams, the above, plus

   range(int from, int to)
   range(int from, int to, int step)


Ignoring naming for the time being:

  - Do these carry their weight?
  - Are we missing any?
  - What related functionality are we missing that might undermine the 
utility of these (e.g., zip)?