sort(xs, @optional test, type)
Return a list containing the elements of the list xs sorted according to test.
Test must be a function that take two arguments and return true if its first
argument must precede its second in the sorted list. Duplicate elements are not removed or rearranged. The default value of
test is number_is_lt which compares two numeric values.
Type specifies the sorting algorithm to use. In the current implementation, type can take
two values: 'quick (for quicksort) and 'merge (for mergesort).
sort([3, 4, 2, 1, 2, 5])
// [1, 2, 2, 3, 4, 5]
list_to_string(sort(string_to_list("hello"), char_is_lt, 'merge))
// ehllo