Add tests in the language

tests/recursive_fib.ang

@@ -0,0 +1,28 @@
+
+fibonacci_numbers := [
+    0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377,
+    610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657,
+    46368, 75025, 121393, 196418, 317811, 514229, 832040,
+    1346269, 2178309, 3524578, 5702887, 9227465, 14930352,
+    24157817, 39088169, 63245986, 102334155
+]
+
+func fib(n) {
+    if n < 2 {
+        return n
+    }
+
+    return fib(n-1) + fib(n-2)
+}
+
+x := 0
+while x < fibonacci_numbers.length() {
+    n := fib(x)
+
+    print("assert ")
+    print(n)
+    print(" == ")
+    write(fibonacci_numbers.at(x))
+    assert(n == fibonacci_numbers.at(x))
+    x = x + 1
+}