Support an array of sheets and/or a gdrive link

[tayloramurphy]

Instead of having to specify multiple pipelines, it might be useful to accept an array or a google drive folder with sheets in it. This would be similar to Fivetran's magic drive https://fivetran.com/docs/files/google-drive

[ReubenFrankel]

Multiple sheets was addressed by #10. Leaving this issue open for the proposed Google Drive feature.