[Issue249] Support for ArrayBuffer in Filer.Buffer

1. Added proxy Buffer constructor for Filer.Buffer.
2. Added tests for new Filer.Buffer.
I see.  Let's do both:

```js
function FilerBuffer (subject, encoding, nonZero) {
  if (subject instanceof ArrayBuffer) {
    subject = new Uint8Array(subject);
  }

 Buffer.call(this, subject, encoding, nonZero);
}
FilerBuffer.prototype = Object.create(Buffer.prototype);
FilerBuffer.prototype.constructor = FilerBuffer;

// Also copy static methods onto ctor                                                                                                             
Object.keys(Buffer).forEach(function (p) {
  if (Buffer.hasOwnProperty(p)) {
    FilerBuffer[p] = Buffer[p];
  }
});
```

Then we get proper inheritance + static members.