e4_filecut_intervals: Filter datasets for a Datetime start + end
In wearables: Tools to Read and Convert Wearables Data

A function to determine how many intervals should be created. The question is at what time do you want the filecut to start, what should be the period that you want separate files for, and what should the interval be?

1	e4_filecut_intervals(time_start, time_end, interval)

`time_start`	User input start time in the character format "yyyy-mm-dd hh:mm:ss" / e.g., "2019-11-27 08:32:00". Where do you want the file cut to start?
`time_end`	User input end time (same format as time_start)
`interval`	# Interval: User input interval (in minutes/ e.g., 5) What is the duration of the interval you want to divide the period into? For example, the paper by de Looff et al. (2019) uses 5 minute intervals over a 30 minute period preceding aggressive behavior. The 5 minute interval is chosen as for the calculation of some of the heart rate variability parameters one needs at least 5 minutes of data, but shorter intervals are possible as well, see for instance: Shaffer, Fred, en J. P. Ginsberg. ‘An Overview of Heart Rate Variability Metrics and Norms’. Frontiers in Public Health 5 (28 september 2017). https://doi.org/10.3389/fpubh.2017.00258.