Early abort for forEach, peek multiple

Adds the capability to peek at multiple entries at the head of the
queue. I didn't have to change QueueFile, as its forEach already can
avoid reading bytes, but this optimization to abort early saves some
object creation.

Added new methods and an interface, deprecated the old code.  Not a
breaking API compatability change.
Merge pull request #61 from pforhan/pforhan/scan

Early abort for forEach, peek multiple