Add example of execution limits using fuel consumption (#2869)

* Add example of execution limits using fuel consumption

* run rustfmt

* Use a more naive WAT implementation

* Catch error and return cleanly

* Add a C example to demonstrate fuel consumption

* Add error handling for add_fuel

examples/fuel.wat

@@ -0,0 +1,13 @@
+(module
+  (func $fibonacci (param $n i32) (result i32)
+    (if
+      (i32.lt_s (local.get $n) (i32.const 2))
+      (return (local.get $n))
+    )
+    (i32.add
+      (call $fibonacci (i32.sub (local.get $n) (i32.const 1)))
+      (call $fibonacci (i32.sub (local.get $n) (i32.const 2)))
+    )
+  )
+  (export "fibonacci" (func $fibonacci))
+)