Extend Function.prototype for Fibers

Allow to use Fibers in context...

Example
```javascript
(function() {
 console.log( (require("fs").readdir.toSync)(".") );
}).asFiber;
```

<b>asFiber</b> extension

before
```javascript
(require("fibers")(function() { /* function code */ })).run()
```
after
```javascript
(function() { /* function code */ }).asFiber
```
<b>toSync</b> extension

before
```javascript
(require("fibers/future").wrap(asyncFunction))(asyncArguments).wait()
```
after
```javascript
(asyncFunction.toSync)(asyncArguments)
```