Handle nested mocked values

As the title says, when there are nested callable values, I would expect those to be typed as mocked values too.

interface ResourcesApi {
    get(id: string): Promise<any>
}

interface Api {
    resources: ResourcesApi
}

const api = mock<Api>()

// The next line will get a type error because `get` isn't mocked.
api.resources.get.mockReturnValue(true)

Thoughts?

[marchaos]

Yep, looking to add support for deep mocks. Will see if I can add support for this without the need for a extra arg

[marchaos]

Merged this - currently opt in - will update the readme