Add scan operators about lightweight-stream-api

[dalewking]

So as an example:

IntStream.iterate(1, i -> i + 2) // odd positive integers
    .scan((a,b) -> a + b)

would be a stream with 1, 4, 9, 16, 25 ... (i.e. the perfect squares)

[dalewking]

The value member variable you introduced in the fix is not necessary. In the methods with no seed it can be a local variable. In the case with the seed it is just a copy of next