Potentially implement range syntax for array command

[sdimitro]

This is outside of whatever exists in the new member command introduced here #17 . Some of that infrastructure could be reused depending of how we want to design this. And interesting idea would be to also have an array command that uses Python-like index syntax to get slices our of lists (e.g. array [3:-1])

[sdimitro]

Besides member mentioned above we recently merged the array command here -> https://github.com/delphix/sdb/commit/b55ca4a193605da0b3e12dca8b1fc0dc9982c088 . Renaming this isssue to have a more specific title.