Seperate exact calculation, fix precalculated data generation typo/bug

[toddytharmonkey]

• The exact calculation for the precalculated data has now been moved into its own python file.
• patched a typo in precalculated_distribution that uses a wrong tfim variable g=.2 instead of g=1 like in the main body of the code. Now g=1 everywhere and the .json file has been recreated.
• Also generally perform housekeeping, like adding documentation.