Create 20_Variations.cs

20. Write a program that reads two numbers N and K and generates all the variations of K elements from the set [1..N].
    Example:	N = 3, K = 2 -> {1, 1}, {1, 2}, {1, 3}, {2, 1}, {2, 2}, {2, 3}, {3, 1}, {3, 2}, {3, 3}