column types not consistent in etox_targets()

[Aariq]

etox_targets() returns a list of data.frames (and URLs for microattribution). It is not easy to bind the data.frames together because at least the Duration column is sometimes character and sometimes integer.

> library(webchem)
> library(purrr)
> library(dplyr)
> etox_data <-etox_tests(c(8668, 8494))
Querying https://webetox.uba.de/webETOX/public/basics/stoff.do?id=8668
Querying https://webetox.uba.de/webETOX/public/basics/stoff.do?id=8494
Warning message:
In FUN(X[[i]], ...) : NAs introduced by coercion
> map(etox_data, ~pluck(.x, "res")) %>% bind_rows()
Error: Can't combine `..1$Duration` <character> and `..2$Duration` <integer>.

P.S., this would be a breaking change, but wouldn't it be better for the output to just be a single tidy dataframe with the URLs as an additional column or stored as an attribute?

[Aariq]

the fix is to provide read.table() with a colClasses argument at line 401. Probably also affects etox_targets()