added fakultaet.c function

src/fakultaet/fakultaet.c

@@ -1,6 +1,13 @@
 #include <stdio.h>
 
 int fakultaet(int n) {
+	if (n == 0 || n == 1)
+		return 1;
 
+	int result = 1;
+	for (int i = 2; i <= n; i++) {
+		result *= i;
+	}
 
+	return result;
 }