@param should have final say if a parameter is optional or has a default

A the moment, this:

```js
/**
* An example.
* @param {Object} options Options.
* @param {FooOptions} options.fooOptions Foo options.
* @param {BarOptions} options.barOptions Bar options.
*/
const example = ({ fooOptions, barOptions } = {}) =>
compose(foo(fooOptions), bar(barOptions))
```

Incorrectly renders with options being optional, due to the JS `= {}` syntax taking priority over the `@param`:

In this example the user must provide options to the `example` function, because the `foo` and `bar` function options are non-optional. The `= {}` is only there for more elegant error handling by allowing validation to happen inside `foo` and `bar`.

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