Feature request: use -c syntax for descr "show" argument

[martinamorris]

First, many thanks for all your packages -- they fill an important gap, and are nicely integrated into the tidyverse workflow.

I'm using the descr fcn, and would like to remove 2 of the summaries. It would be much easier to specify the complement

show=-c("type", "label")

than to specify the list of summaries desired. That would also make the syntax consistent with other base R usage. There may be other places in the package where this could also be used, but this is the one I ran across in my work.

thanks!