Added ion() and show() commands to plot_fit
Changed the baseline ordering of states
MCMC file to globally fit the NBD model to all NBD data
Added obj func calc for c62 as well
Trashed the NBD MATLAB code generation approach
Minor changes to docstring for nbd_model
A parallel insertion model for NBD

Also a shared model file with Monomer, Observable, and Parameter
declarations that are shared across models.
Refactored NBD MCMC and NBD linear model

NBD linear model now uses shared component declarations.
Added extensive introductory documentation to core.py