function to export posterior summaries from an mcmc object to a table
# S3 method for mcmc
table(MCMC, file = NULL, type = "csv", a = 0.05)
An mcmc object with columns referencing different parameter types (column names are used for plotting labels)
A file name to ouput to (including path); if null (default), outputs to screen
What type of table to produce (either "csv" or "tex")
Value to use for credible intervals. For example, alpha=0.05 results in 95% credible intervals