Add flag for defining path/value separator in json_info.

[SpicyLemon]

Currently, json_info uses = as the separator between the path and info (if both are being displayed). It'd be nice to be able to define this string, though.

My initial use case would be to make it easier to separate the paths and info into columns using the column command. It'd be something along the lines of json_info -r --separator '~' -f foo.json | column -s '~' -t. Technically, this can also be done using json_info -r -f foo.json | sed 's/ = /~/' | column -s '~' -t though, so maybe it's not all that needed for that.

But who knows. Maybe someone would like to use ': ' there instead, or maybe something else.

I guess maybe this is just a nice-to-have at some point.