Added first draft of sample-based sliding window.
Only skip data on each call to next() in iterator.
No need for a one-shot iterator.
Fixed bug where added data wouldn’t be stored if no varargs supplied.
Forgot to return typed Builders in method chaining calls.
Added appropriate tests for SampleBasedSlidingWindow.
Merge branch 'sample-sliding-window'

Created first SampleBasedSlidingWindow class. See #8.