replaced single-shot HTTP requests with retry logic

[jameslamb]

Thanks for this project!

In this PR, I'd like to propose swapping out calls to httr::POST(), httr::HEAD() etc. with httr::RETRY(). This will make the package more resilient to transient problems like brief network outages or periods where Drill is briefly unavailable. In my experience, using retry logic almost always improves the user experience with HTTP clients.

I'm working on chircollab/chircollab20#1 as part of Chicago R Collab, an R 'unconference' in Chicago.

[hrbrmstr]

This is brilliant! #ty!!!

Can you also update DESCRIPTION to add yourself? I need to tweak a few other things the REST API supports now and shld be sending this to CRAN in May. Wld def like to have you in for that push.

[jameslamb]

@hrbrmstr sure, I'll do that right now! I'll take a look at the other issues too, maybe there are other things I can help with.