math: digits function; SqrtTau; extra spaces; re writed doc's to correct form; test for factorial

vlib/math/math_test.v

@@ -13,3 +13,21 @@ fn test_lcm() {
 	assert math.lcm(-2, -3) == 6
 	assert math.lcm(0, 0) == 0
 }
+
+fn test_digits() {
+	digits_in_10th_base := math.digits(125, 10)
+	assert digits_in_10th_base[0] == 5
+	assert digits_in_10th_base[1] == 2
+	assert digits_in_10th_base[2] == 1
+
+	digits_in_16th_base := math.digits(15, 16)
+	assert digits_in_16th_base[0] == 15
+
+	negative_digits := math.digits(-4, 2)
+	assert negative_digits[2] == -1
+}
+
+fn test_factorial() {
+	assert math.factorial(5) == 120
+	assert math.factorial(0) == 1
+}