transplantr 0.2.0

added liver transplant survival predictor functions:
- Liver DRI
- ET-DRI (Eurotransplant variant of DRI)
- SOFT Score (Survival Outcomes Following Liver Transplantation)
- BAR Score (Balance of Risk)
- Pedi-SOFT Score
added three further eGFR calculators
- Nankivell equation
- Nankivell-SPK equation
- Walser equation
bugfix to UK KDRI function (was not including effect of donor hypertension)

transplantr 0.1.0