Add unit tests for sentence segmentation regex.

This includes moving the regular expression to a constant so that it
is available for testing.
Prevent sentence break at e.g. and i.e.
Fix typo in README
Add tests for paragraph segmentation regex, and update regex.

This includes moving the regex to a const on the segmentation class
to make it available for testing, and updating the regex to pass all
added tests.
Merge branch 'segmentation'