define_day_indices      Generate sequential day indices from ISO 8601
                        timestamps
get_cadence_bands       Calculate minutes and steps spent in cadence
                        bands
get_cadence_peaks       Calculate cadence peak metrics
isGGIRoutput            Check if a directory is a valid GGIR output
                        folder for stepmetrics
readFile                Read and standardize minute-level step data for
                        one participant
step.metrics            Calculate and export daily and person-level
                        step and cadence metrics
