run_MCMC: Do a metropolis chain
In jmzobitz/SoilModeling:

run_MCMC Does a complete MCMC parameter estimation

1 2	run_MCMC(param_file_name, model_in, data_in, join_key, results_file_name, out_file_name, mcmc_parameters)

`param_file_name`	file name (as a string) of where the default parameters are located
`model_in`	the name of the model we are using
`data_in`	input data we use to compare in the likelihood function.
`join_key`	The name of the variable we will join to data_in when doing likelihood
`results_file_name`	The file name (as a string) where the final MCMC results will be stored.
`out_file_name`	The file name (as a string) where we log various info as the mcmc proceeds
`mcmc_parameters`	a data frame of how we want to estimate (can be mcmc_superfast or mcmc_defaults)