Add support for vectorized paths

[colearendt]

For programming, it would be nice to allow for vectorized paths. At present, it is possible to workaround with do.call, but this does not work nicely in a pipeline.

I think a useful (and tidy) way of implementing would be the tidyeval framework that was recently added to the rlang package.

• Bonus : If it is possible to somehow vectorize (or automate) type-determination (like the readr package does), I believe that would make for a nice solution to the typing required for spread_values!

[colearendt]

Some thoughts on a readr-like approach:

• Determine names, handle missing or duplicates... Maybe handle recursion first to get all possibilities for consistent naming, rather than deduplicating while recursing
• Generate json_spec (requires json_spec class). Some methods for this: json_skip,json_factor,json_dbl,json_chr,json_int,json_lgl,json_date,json_datetime,json_only... naming convention up for grabs using the purrr or the readr conventions
• Execute json_spec to spread out the JSON as designated.

The hope is that this could be combined together into a single spread_json function which has nice guess behavior like spread_all, but is also easily standardized like spread_values, but with less typing.