Draft: Add a --json flag to output json.

[jorikvanveen]

This PR adds a --json flag which causes lsd to output the Metas as JSON.

It's a basic proof of concept I put together in an evening, so there are some .unwrap()s and rough edges. It's meant to show what I imagine this feature to look like so you can decide whether this is something you actually want implemented in lsd. If it is I can start working on a more serious implementation.

Why?

Combining this flag with something like nushell allows users to create ls aliases that output structured nu data but still look pretty.

For example, this alias:

def --wrapped ls [...rest] {
        lsd ...$rest --json --icon always --icon-theme fancy --color always
        | from json
        | get 0.content
        | select type display size date
        | update date {|row| $row.date | into datetime}
        | update size {|row| $row.size | into filesize}
      }

results in this output:

and you can then use other nushell operations to do something with this data:

TODO

• Use cargo fmt
• Add necessary tests
• Update default config/theme in README (if applicable)
• Update man page at lsd/doc/lsd.md (if applicable)

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