MTLR v0.2.0

MTLR 0.2.0

• Added an option to optimize concordance instead of the log-likelihood when selecting a value for C1 in mtlr_cv.
• Removed ellipses from create_folds since it's easy to use type instead of foldtype when passing in arguments.
• Fixed a bug where if all data was left or right censored an error was thrown since there was no interval censored data.
• mtlr_cv output is not best_C1 and not bestC1 to match the documentation.
• Removed usage of Rcpp data structures inside MTLRHelper.cpp. This was not needed and just wasting time when transferring them to armadillo structures.
• A number of printing fixes were made, e.g. printing out all variable names at once instead of one at a
  time for warnings and actually printing results when verbose = T for mtlr_cv.
• When biases are trained they now assume the data are uncensored.