Expose orderBy as a parameter when listing documents

[michaelcho]

Is your feature request related to a problem? Please describe.
I would like to expose the list of spreadsheets to the user with a different orderBy than the default recency which is hardcoded here.

Describe the solution you'd like
Either:

1. the orderBy parameter is passed down through the client methods for spreadsheet_titles() and spreadsheet_ids()
2. OR at the very least, change the hardcoding to recency desc. I think most users would want to see the most recent files rather than the oldest files?

Any other info
I think I can make a pull request for this enhancement, so let me know if this would be accepted and I can tidy up the tests etc. Otherwise I'll just leave it on my forked version of the repo.

Thanks!