Similar to getwd() and setwd(),
these functions get and set the folder ID of the working directory
at box.com.
This folder ID is also stored in boxr_options().
box_setwd(dir_id)
box_getwd()numeric or character, folder ID at Box.
box_getwd()numeric, ID for working folder at Box.
box_setwd()invisible(NULL), called for side-effects.
box_ls() to list files in a Box directory,
box_fetch()/box_push() to download/upload directories from/to Box