charts from Google Sheets

[kangkyu]

editor = Gslide::Editor.new(token)
d = Gslide::SpreadsheetDraft.new(auth: editor)
s = d.create(options)
# => <Gslide::Models::Spreadsheet ...
s.batch_update({
  requests: [
    add_chart: {
      chart: {
        spec: {...},
        position: {
          new_sheet: true
        }
      }
    }
  ]
})
s.get_sheets