(JSON) Add support for 2D array exports of sheets

[Synthoid]

Add support for exporting sheets as 2D arrays of row values. See below for example:

[
  ["header1", "header2"],
  ["row1_col1_value", "row1_col2_value"],
  ["row2_col1_value", "row2_col2_value"],
]

[zachguo]

Can you point it to me where I should change to enable this? I may submit a PR.