Adding unit tests for sorting functions, and improving readability on some sorting algorithms (#784)

* Adding variable to fade out ambiguity

* More readability on merge sorting algorithm

* Updating merge_sort_fastest description and explaining why

* Adding tests file with imports

* Standardazing filenames and function names

* Adding test cases and test functions

* Adding test loop

* Putting 'user oriented code' inside main condition for having valid imports

* Fixing condition

* Updating tests: adding cases and todo list

* Refactoring first euler problem's first solution

sorts/radix_sort.py

@@ -1,4 +1,4 @@
-def radixsort(lst):
+def radix_sort(lst):
     RADIX = 10
     placement = 1