There are a number of computational changes in this commit.

1. the MH algorithms now work with logs instead of raw probabilities.
2. the proposal variance for the MH alg for fixed coefficients is now updated based on the acceptance rate.
3. the hb function now allows for constraining the sample-level variances in the D file

I've also added a tools folder to contain any tools that are constructed. I've added a distribution converter which calculates the moments of the distributions for the random parameters based on the markov chains.