Returns rb3 package cache directory
Value
a string with the file path of rb3 cache directory
Details
In order to set a default directory for cache, which is a good idea for those
who want to increase data historically, the option rb3.cachedir can be
set.
Once it is set, the defined directory will be used as the default cachedir.
Examples
cachedir()
#> [1] "/tmp/Rtmp3rDxqn/rb3-cache"
