Added unit tests for sorting algorithms.

test.py included standard tests for each algorithm implemented so far.
Fixed usage of min/max in counting_sort.

Previously, counting_sort referenced variables called min and max, rather than min_value and max_value. Instead, they resolved to the builtin functions min and max, causing an error.
Counting_sort now correctly handles single value or empty dataset input

A dataset of less than 2 elements now simply returns.
Radix_sort now correctly handles single value or empty dataset input

A dataset of less than 2 elements now simply returns.