add httr::RETRY wrapper to large query fetching

[sampoves]

Failsafe for error 429 Too Many Requests

[pitkant]

@sampoves thank you for the contribution! I tested it with your example code from #281 and everything worked like a charm. The package checks also passed.

Just as a minor note for possible future improvement (not something you need to fix, this works works after all) maybe the message "Request failed [429]. Retrying in 60 seconds..." might look menacing to a new user and prompt them to cancel the query?

> res <- pxweb::pxweb_get_data(pxweb_url, pxq)
  Downloading large query (in 36 batches):
  |===========================================================================                             |  72%
Request failed [429]. Retrying in 60 seconds...
  |========================================================================================================| 100%

But as I said it's good enough as it is.

@MansMeg I can make another PR with some package housekeeping like

• bumping the version number
• adding Sampo as a package contributor
• fixing the double header in citation("pxweb")

and maybe the new version could be submitted to CRAN? I don't know when CRAN Christmas break starts but maybe there's still time before that.

[sampoves]

@pitkant Thank you for accepting the contribution 💫 Also, thank you for your continued work on this important package.

[sampoves]

Sorry for the mess-around, thought it may not be a good idea to close the pull request myself.

[pitkant]

Yeah I think it's a good idea that changes to pxweb_get are merged from this PR so code contributions are attributed correctly.

[MansMeg]

Thanks! Changing to RETRY might be a good idea. However, I think we need to enable the user to govern this a little more, ie using ellippsis and using try = 1 as default in pxweb_get.