Add apc information

[yjunechoe]

The apc_list and apc_paid fields in a Work object are now returned as a single data frame in the apc column of the df output

devtools::load_all()
x <- oa_fetch(identifier = c("W1964141474", "W1963991285"))
x$apc
#> [[1]]
#> [1] NA
#> 
#> [[2]]
#>   type value currency value_usd provenance
#> 1 list  4480      USD      4480       doaj
#> 2 paid  4480      USD      4480       doaj

[yjunechoe]

(I'm actually very puzzled by the testthat error I'm getting and can't seem to figure it out - will return to fix at a later time)

[trangdata]

(I'm actually very puzzled by the testthat error I'm getting and can't seem to figure it out - will return to fix at a later time)

Very strange message indeed! We can always wait a couple days to see if this resolves itself on the OpenAlex's end.

[trangdata]

I had to modify some tests but it should be good now.

[yjunechoe]

Thanks for picking this back up for me!