[WIP] API refactor

[rish987]

Addresses #151. I'm making this PR right away so you can stay updated on my progress, and I will try to keep the commits as atomic as possible. Feel free to chime in anytime if something doesn't look right to you.

[ggandor]

Okay, thanks!

Just a quick glance:

First, let's leave Telescope out of this PR completely, as this refactor is much more general, and limit additions to the documentation to the actual API changes, if there will be. (An extension plugin/gist/snippet can be shared anytime.)

I don't understand the motivation behind moving with-highlight-chores into light-up-beacons; the very point of the macro is to wrap the more specific stuff with the general chores, and ensure the proper ordering in a foolproof way (and even with messed-up extmark priorities): cleanup first, backdrop, doing stuff, and then, after everything, calling redraw.

That said, yep, we should probably introduce "ranges" as a concept somehow. But that should cover search, backdrop & beacons too.

Fennel tips:

• shorthand for {:foo foo :bar bar} is {: foo : bar}
• {} tables are usually used (here) for passing optional values to functions, there's no need to redundantly mark "maybe" values in them ({:?foo bar})

[rish987]

Hey thanks. You will have to bear with me for a while as I am learning Fennel hahaha. I had moved with-highlight-chores into light-up-beacons with the intention of eventually making that the beacon() API function (because you wouldn't want to make the user have to call with-highlight-chores themselves). But I have reverted that for now, we can think about it later. I'm going to focus first on extracting the select() function (and target state).

[rish987]

Should be okay since it looks like the label will be nil in this case anyways