Add emote event definitions

[benclifford]

These are intended for foreground apps to signal to other components (for example hexpansion drivers) that something interesting, good or bad, happened in the user interface, so that the other component can present that in its own way to the user.

Guidelines for use:

Only send emotes when you are the foreground app: these events are intended to be UI output like writing to the screen is.

Send at most a handful of emotes per minute. These events might generate relatively long behaviours on the order of a few seconds, for example playing a short jingle on an audio hexpansion.

[sodoku]

I think it would be good to also add this to the docs.

[benclifford]

I think it would be good to also add this to the docs

@sodoku that's in the docs repo, not this one, right? (so can't go in this PR?)

I'm happy to add that though -- I wrote the guidelines part of the commit message as me beginning to think about what to write.

[sodoku]

@benclifford yes, in the docs repo. The eventbus is documented here: https://github.com/emfcamp/badge-2024-documentation/blob/main/docs/tildagon-apps/reference/eventbus.md and how to use the button events here: https://github.com/emfcamp/badge-2024-documentation/blob/main/docs/tildagon-apps/reference/badge-hardware.md#custom-usage

Not sure where exactly the emote events should go, but I think especially the guidelines should be documented if we want people to follow them. Also the more discoverable this emote events are the more people might use them :)

[benclifford]

@sodoku wrt your comment

Not sure where exactly the emote events should go

I made this PR to create a place for documenting built in events: emfcamp/badge-2024-documentation#282

Then I can document emote events in a subsequent PR.