Merge pull request #5 from KellyBlack/dev

Candace and Linton Code
Merge pull request #6 from sweenee/dev

Dev
repeated Z to estimate distribution
first draft of INS SDE approximations
simple stochastic integral approximation
fix for left hand sum
first draft of second model approx
iterations of Z with left hand sum
Merge pull request #7 from KellyBlack/dev

Dev
switch to left hand sum
Merge pull request #13 from sweenee/beth_dev

all three of our changes with left hand sum