Fixed division and log errors

Sometimes I hate implicit typing.

Not certain if prob are correct yet but errors were fixed. Python 2.7
assumes integer division unlike Python 3. To force float division,
future import was done.

With float divisions, prob calculations ceased to be zero, fixing math
domain errors on log calcs. Added try statement to log calc anyways to
catch any exceptions that might occur.

Probabilities now are never zero as expected.

TODO: Check sum of probabilities to ensure correctness.