Add a segmented control accessory type

[yeahphil]

Here's a segmented control accessory, done in the same style as the switch accessory.

I used Static for a table that had a segmented control, and ended up going back and adding it to the library for my convenience. No problem if the idea behind this library is to stay small and not have lots of built-in accessories, but please feel free to include it!

Note that this will probably have the same behavior described in #135

[dmiluski]

Hi @yeahphil , thank you for taking the time to PR this.

As you aptly point out: that this will probably have the same behavior described in #135

As long as that is a known point, happy to include this if it helps your use case out. Given that this can be handled by updating a given row accessory, I think this can move forward. Letting this simmer over the weekend to see if there are any other feedback items, but I'll likely merge this in on Monday.

[yeahphil]

Hi @dmiluski, thanks for taking a look! I'm set either way but thought it might be nice to contribute this back to the project. Whether it should be merged might depend on whether you'd like a bigger set of built-in controls, or would prefer Static users add any accessories beyond the basics using the .view case.

If you think the latter makes more sense, I'd be happy to add a quick guide to making accessories to the docs when I have a few free minutes.