using jsonlite to automatically build payloads

[jmobrien]

Suggested change--still needs tests written, but thought I'd go ahead and put it in the pipe for review. So far seems to work fine.

• Uses toJSON from package jsonlite for automated construction of payloads, eliminating the massive manual build using a bunch of ifelses and paste. qualtRics has imported functions from jsonlite for quite a while now, so this doesn't add any new dependencies.

• purrr::discard drops any null parameters when building, as qualtrics API doesn't like actual json nulls or empty sets.

• Retains original technique for formattingstart_date and end_date to fit ISO 8601 as expected (https://api.qualtrics.com/docs/dates-and-times). Looking ahead, though, could be easier now to set up more flexible handling of start and end times, useful now that since-last-response request functionality is gone, see last_response still fetches all responses #153.

[juliasilge]

This is fantastic @jmobrien! Thank you so much. 💯

[jmobrien]

Glad it helped. As mentioned above, next steps might be for someone to think about how best to have this tool accept the standard date/time output used by the readr tools we're currently employing in read_survey for formatting csvs and assigning data types to variables.

I played around with it for a bit earlier before submitting but didn't see a standard tool that could do date+time with the "T" separator, and I didn't feel confident about homebrewing something. Plus I wasn't sure how to implement timezones in a way that made the most sense and properly considered implications, if any, of how the useLocal flag was set.

[juliasilge]

If you want to open an issue with your ideas and any summary of what you tried, we can save that for later.

[jmobrien]

Can't say I spent a ton of time on it, but I'll write a few lines.