json-shell: more complex key targets

[pfuntner]

I would like a way to express more complicated key targets to json-shell:
- cd /foo
- cd foo/bar
- cd ../foo
- cd ~- or cd -?

None of these can be done right now. You're limited to a single key without slashes. You can enter a slash but it's assumed that you're expressing a single key and the slash is part of the key.

These could also apply to cat and describe.