makefile: added variables
adding an example stan_fit_test
updating makefile for testing c++ code
testing do_print()
fixing makefile for c++ tests
updated implementation of rstan's do_print() to use stan::common::do_print()
refactor: adding test scaffolding for print_progress
refactor: print_progress() -- changing implementation
refactor: removing rstan::do_print(); replacing with stan::common::do_print()
refactor: consolidated do_print() and print_progress()