Expose print, summary and plot methods

[grantmcdermott]

Thanks for putting this package together.

It would greatly improve the user experience if we could add some generic methods for viewing and manipulating the estimated object. For example, the automatic post-estimation plot—via the internal/hidden plot_bootstrap_result function—is nice, but doesn't lend itself to a programmatic workflow. Could we not expose this internal function to the user so that they could run it on an object afterwards?

I'm happy to contribute some of these methods via pull request. But this repo doesn't seem to be actively maintained, so it would be great to know that someone will at least take a look at any suggestions before I commit time to a PR.

Thanks again.