SecretNumberTests.cs (GuessMe method fully tested)

Tests Added:
public void TestGuessMe_ShouldHave_0CowsAnd0Bulls()
public void TestGuessMe_ShouldHave_1CowAnd0Bulls()
public void TestGuessMe_ShouldHave_0CowsAnd1Bull()
public void TestGuessMe_ShouldHave_2CowsAnd1Bull()
public void TestGuessMe_ShouldHave_1CowAnd2Bulls()
public void TestGuessMe_ShouldHave_2CowsAnd2Bulls()
public void TestGuessMe_ShouldHave_3CowsAnd1Bull()
public void TestGuessMe_ShouldHave_4Cows()
public void TestGuessMe_ShouldHave_0Cows3Bulls()