Counting into bins

You will write three small functions that turn a list of values into the numbers behind a histogram: the counts in each bin, the relative frequencies and the frequency densities.

The idea. A bin from left to left + width holds a value x when left <= x < left + width, so an edge value goes into the bin above. A relative frequency is a count divided by the total. A frequency density is a count divided by the width.

Your tasks.

1. Finish bin_counts(data, start, width, n_bins). Return a list of n_bins counts.
2. Finish relative(counts). Return each count divided by the sum of the counts.
3. Finish density(counts, widths). Return each count divided by the width of its bin.