feat: Allow 'multiple' Listbox options

[chaseweaver]

Added

• multiple as a Listbox option allowing a multi-select
• Listbox example using multiple

Note

I needed this for a project I'm migrating over to Svelte (from Vue), so I make a quick fork to implement the multiple option that HeadlessUI currently has (near 1:1 implementation).

I took a glance at #47, #57, and #63 where you mentioned doing a bit of a rework. If this PR won't work because of that, no worries.

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Name	Status	Preview	Updated
svelte-headlessui	✅ Ready (Inspect)	Visit Preview	Nov 6, 2022 at 3:09PM (UTC)

[sureshjoshi]

Small quality of life improvement for anyone using this PR - you'll want to probably wrap the $api.closeListbox(); call in ListboxOption.svelte with a if ($api.mode === ValueMode.Single) check so it stays open during multiple clicks.

[chaseweaver]

Small quality of life improvement for anyone using this PR - you'll want to probably wrap the $api.closeListbox(); call in ListboxOption.svelte with a if ($api.mode === ValueMode.Single) check so it stays open during multiple clicks.

Ah, good call! Added 👍

[philmas]

@rgossiaux, Is it possible to select multiple listbox options in version 2.0 of svelte-headlessui?