Added section to emphasize difference between exceptions and assertions#1

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Commits on Nov 8, 2016

added section to clarify exceptions vs assertions
Arjun Biddanda
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Commits on Nov 9, 2016

revised learning objectives to be active voice and an example on when to use exceptions rather than assertion
Arjun Biddanda
committed

Commits on Nov 11, 2016

revised typos
Arjun Biddanda
committed