factor out moving over loci to an iterator to allow for folds
adding private modifier to sliding window iterator
adding tests for window fold
additional comments on SlidingWindowsIterator
update to remove mutating windows in has next and do so in next
move sldiingwindow classes to correct package folder
a few line length and style cleanups
more long lines and style nits
ruthlessly privatize SlidingWindowIterator methods
experiment: type alias `PerSample` for `Seq`