0.0.1, 12/30/2017, Minimum viable LubDub: PlotHRV works well enough.
0.0.1.2, 12/30/2017, Added SDNN and NN50 calculators.
0.0.1.4, 12/31/2017, Improvements to rr_normalization function (allow drop_values boolean argument).
0.0.1.5, 12/31/2017, Measurement (new): rounds up all the usual analysis for RR intervals. Added convenience functions for loading RRs from files.
