shim directly when in the browser

So I can understand not wanting to merge #8, but one of the unfortunate things about the existing wzrd.in script is that it doesn't actually shim the variables on the `window` object, which is what you'd probably expect a shim library to do.

So would you be amenable to a change like this?  Else you could recommend in the readme that folks roll their own:

```js
    var keys = [
      'ArrayBuffer',
      'DataView',
      'Float32Array',
      'Float64Array',
      'Int8Array',
      'Int16Array',
      'Int32Array',
      'Uint8Array',
      'Uint8ClampedArray',
      'Uint16Array',
      'Uint32Array'
    ];

    for (var i = 0; i < keys.length; i++) {
      var key = keys[i];
      if (!(key in window)) {
        window[key] = window.typedarray[key];
      }
    }
```