pass in a raw pixelBuffer to the open command

Referencing my previous pull request #84 - but now on the 0.0.6 branch
`width` and `height` need to be positive integers.

Can replace both of the following conditions

```Javascript
if(!type.width) {
    throw Error("Missing width");
}
if(typeof type.height !== "number") {
    throw Error("Height must be numeric");
}
```

With:

```Javascript
if (!(type.width === parseInt(type.width) && type.width > 0)){
    throw Error("Width must be a positive integer");
}
```

This will cover both cases where `type.width` is undefined, and not of the correct type.