possible list: * [bchron](https://cran.r-project.org/web/packages/Bchron/index.html) * [calpal](http://monrepos-rgzm.de/forschung/ausstattung.html#calpal) * [calibrator](https://github.com/ISAAKiel/calibrator) * [bcal](http://bcal.shef.ac.uk/) * calib (dead?) * name it
