Add a `--format=json|ndjson` option to `CLI::ModelCommand`

[postmodern]

It should be possible to output queried models in JSON and ndjson formats.

[moozzi]

I though about adding new classes and one method to the Printing module like:

class DefaultPrinter
  def print(records)
    records.each(&method(:puts))
  end
end

class JSONPrinter
  def printer(records)
    p records.as_json
  end
end

class NdjsonPrinter
  def print(records)
    records.each { |record| p record.as_json }
  end
end

def self.for(format)
  case format
  when :json
    JSONPrinter.new
  when :ndjson
    NdjsonPrinter.new
  else
    DefaultPrinter.new
  end
end

and instead of calling print_record we could create print_records method that could look like this:

def print_records(records)
  printer = Printing.for(options[:format])
  printer.print(records)
end

What do you thing @postmodern ?

[postmodern]

Any printing needs to be done in the CLI command class itself, since a custom stdout object can be passed in to override the default $stdout, such as when testing the output of commands.

let(:stdout) { StringIO.new }
let(:command) { TestCommand.new(stdout: stdout) }