add an example comparing/testing undate against partial dates & durations in Shakespeare and Company Project dataset

[rlskoeser]

create a jupyter notebook that loads S&co events dataset and installs undate; should go in our examples directory

for events with duration, test parsing start and end with undate and comparing the duration from undate with that in the public dataset

any discrepancies? if so, can we figure out why?

[rlskoeser]

notebook added in #36