add iterative and recursive fibonacci functions

benchmarks/fib_dynamic.cdc

@@ -17,5 +17,5 @@ fun fib(_ n: Int): Int {
 
 access(all)
 fun main() {
-    assert(fib(14) == 377)
-}
+    assert(fib(23) == 28657)
+}

benchmarks/fib_iterative.cdc

@@ -0,0 +1,19 @@
+access(all)
+fun fib(_ n: Int): Int {
+    var fib1 = 1
+    var fib2 = 1
+    var fibonacci = fib1
+    var i = 2
+    while i < n {
+        fibonacci = fib1 + fib2
+        fib1 = fib2
+        fib2 = fibonacci
+        i = i + 1
+    }
+    return fibonacci
+}
+
+access(all)
+fun main() {
+    assert(fib(23) == 28657)
+}

benchmarks/fib_recursive.cdc

@@ -0,0 +1,12 @@
+access(all)
+fun fib(_ n: Int): Int {
+    if n < 2 {
+        return n
+    }
+    return fib(n - 1) + fib(n - 2)
+}
+
+access(all)
+fun main() {
+    assert(fib(23) == 28657)
+}