segment s splits s into a list of sentences.
It looks for punctuation characters that indicate an
end-of-sentence and tries to ignore some uses of
puncuation which do not correspond to ends of sentences
It's a good idea to view the source code to this module,
especially the test suite.
I imagine this sort of task is actually ambiguous and that
you actually won't be able to write an exact segmenter.
It may be a good idea to go see the literature on how to do
segmentation right, maybe implement something which returns
the N most probable segmentations instead.