Wimpy

- added a `strict` option (default `False`) to `strip_prefix`/`strip_suffix`, which will raise an exception if the substring was not there
- fixed handling of negative `overlap` values in the `chunks` function (thanks to Aran-Fey for the contribution)

Add `is_subsequence` implementation, checks if all items in first appear in second in same order


>>> is_subsequence([1,3,7], range(10))
True
>>> is_subsequence([4,3,7], range(10))
False

- util.chunks
- exceptions.WimpyError

- utils.grouper
- utils.ceiling_division