Allow the user to customise the columns displayed in `py list`

Is your feature request related to a problem? Please describe.
I don't find the default display of py list particularly useful. The aliases take up a lot of space and aren't very helpful (they are easily deducible from the rest of the data). Ideally, I'd like to be able to choose more useful information to display in place of that column.

Describe the solution you'd like
The --format option allows you to display a single data item (--format=exe). That's fine, but it would be nice to be able to choose multiple values. Something like --format=tag,exe.

Describe alternatives you've considered
You can get this sort of report by piping --format=json into jq, or into a custom formatter, but that's fairly clumsy.

Additional context
Alternative to #86. The approach here is probably overkill, but I've filed it as an option in case changing the default format is unacceptable.

まず、py list コマンドの --format 処理を特定し、単一項目の出力を既存の JSON 出力と比較します。tag,exe のようなカンマ区切りの値をどのように解析して表示するかを定義し、複数の選択されたフィールドが要求された順序で現れ、既存の単一値の動作を壊さないことを確認します。