With this commit, we now allow developers to remove the `stream` shim
from browserify/webpack bundles to reduce the final size. Moreover, we re-use
the existing `stream` shim to deduplicate code.

Now, you can use `--dg false --bare` with browserify and

```js
module.exports = {
  node: {
    "stream": "empty",
    global: false,
    process: false,
    Buffer: false
  }
};
```

as webpack configuration, JSZip won't throw an error.

JSZip doesn't need it but `lie` (the `Promise` shim) does. This
dependency is only called when the js runtime doesn't provide a `Promise`.

The minimalist browserify flags (to work in all browsers) are `--no-builtins
--insert-global-vars global` and the minimalist webpack configuration is now

```js
module.exports = {
  node: {
    "stream": "empty",
    global: true,
    process: false,
    Buffer: false
  }
};
```

If the `global` object is not available in the bundle, you will get an
error in old browsers.