Add a noMatchSnapshots option.

[tmeasday]

See #81

Perhaps it would make sense to just allow passing a custom test function, to cover off cases like this and #76?

initStoryshots({
  test(renderedStory) {
     // In my case, just render without looking at the result
     renderer.create(renderedStory).toJSON()

     // For #76, shallow render + snapshot
     const tree = shallowToJson(shallow(renderedStory))
     expect(tree).toMatchSnapshot()
  }
});

[shilman]

Hey @tmeasday

Thank you so much for this PR! We're moving over to a mono-repo, since that makes a lot of sense for a project like this.

We would ❤️ it if you could create a PR here: https://github.com/storybooks/storybook

Please let me know if you have any q's!