* Add optim() in search and update searching algorithm
* Fixed bugs in piecewise models
* Re-calculate the censoring survival estimates with Nelson-Aalen estimate when
there the KM estimates drop to 0 at early times.
* Set robust = FALSE in coxph() to avoid calculating robust variance estimator
when a is extreme.
* Use grid search (rootSolve then optim) in finding a
* Updated piecewise model so `a` is optimized globally
* Added goodness of fit test
* Passed CRAN checks
* Added regression method, `trReg()`