Support more checkbox statuses

[jotaen]

Apart from the currently supported statuses [ ] (open), [x] (checked), [@] (ongoing), and [~] (obsolete), there might be more useful ones.

I think the overall number of statuses should be limited, just so that they can still be memorized relatively easily. To me, there shouldn’t be more than 5 or 6 overall, which – next to the existing ones – would leave room for 1–2 more.

The purpose of this issue is to collect and maintain an overview of potential candidates.

Purpose	Symbol Ideas
“unclear”, “questioned”	[?]	https://github.com/jotaen/xit/discussions/34
“paused”, “on hold”	[.]	https://github.com/jotaen/xit/discussions/42

Note: the requirements for a symbol are:

• It should be somewhat self-explanatory
• It should be language-agnostic, so it should be a symbol, not e.g. the first letter of an English word
• If ever possible, it should be an ASCII character, to ensure that it’s easy to type on every keyboard
• There should only be one canonical symbol per status, so no “aliases”

[clach04]

Refs:

• https://github.com/jotaen/xit/discussions/42
• https://github.com/jotaen/xit/discussions/34

[jotaen]

@clach04 thanks for the refs, I’ve added them to the table above.