haxe.io.Bytes.alloc should initialize the buffer

All nodejs docs show that

``` javascript
new Buffer(length);
```

is **uninitialized**

However,

``` javascript
haxe.io.Bytes.alloc(length);
```

returns an initialized (with 0's) buffer in all targets. While I can't seem to find any documentation to support this, the code in the standard haxe.io.Bytes suggests this to be the case

To maintain consistency, probably should do (at about line 266 in haxe/io/Bytes.hx) :

``` javascript
#elseif (nodejs || nodejs_std)
var a = new js.Node.NodeBuffer(length);
a.fill(0, 0, length);
return new Bytes(length,a);
```

instead of

``` javascript
#elseif (nodejs || nodejs_std)
return new Bytes(length,new js.Node.NodeBuffer(length));
```