Aalen-Johansen estimator survival plots for competing risks survival analysis

This dongle includes two functions for tidying and plotting AJ estimator survival curves for competing risks.

1. tidy_ajcomprsk: Create tidied data tailored for plotting AJ curves.
2. gg_ajsurvplot and gg_ajsurvplot2: create AJ cum-haz curve for the event of interest, without and with one competing event. The former supports both survminer::ggsurvplot and ggsurvfit::ggsurvfit as backend with minimal change to their parameters.

Trinh Dong, 2024