Quartiles and outliers

You will write four functions that find the quartiles, the interquartile range, the outliers and the ends of the whiskers of a box plot. The helper median_of is already written. The checker uses data with an even and an odd number of values.

The idea. Split the sorted data into a lower and an upper half, and leave the median out of both halves when the number of values is odd. $Q_1$ and $Q_3$ are the medians of the halves. The fences are $1.5$ interquartile ranges beyond the quartiles, and an outlier is a value outside them.

Your tasks.

1. Finish quartiles(data). Return $(Q_1, \text{median}, Q_3)$.
2. Finish iqr(data).
3. Finish outliers(data). Return the outliers in increasing order.
4. Finish whisker_ends(data). Return the smallest and the largest value that are not outliers.