`here::u_r()`

[beevabeeva]

First of all, thank you to @krlmlr et al. for this great package. I use it daily.

I have made a pull request for a new function here::u_r (see #77).

Not sure if the contributors prefer to discuss/review it in an issue or in the comments for the PR, so I opened both :sweat_smile: .

I was inspired to submit the PR after keeping (and using) this function locally for a while, but later reading #41, #28 and #19 (and @krlmlr 's replies to them).

here::u_r()

#' Resets here() root to current or target working directory.
#'
#' If no target root directory is specified, the current working directory will be used.
#' There is no need to restart the session
#' 
#' The function is named:
#'     u_r (as in "here::you_are") in reference to:
#'        1. everyone:'WHY ISN"T THIS INCLUDED IN THE PACKAGE!?'
#'           me: 'Well, here you are.'
#'        
#'        2. user:'Start here() at my cwd.'
#'           here:'OK, here you are.' (anastrophe)
#'
#'     u_r (as in "here::user_reset") in reference to:
#'        1. Providing a quick way for a user to reset the root of here().
#'
#'     u_r (as in "here::unload_reload") in reference to:
#'        1. The method used to change the root of here().
#'
#' Q: Why use this when there's RStudio projects?
#' A: There are certain cases where this method is preferable. 
#'
#'
#' @param target_wd `[character(1)]`\cr
#'   The target root directory to start here() from.
#'   If no target root directory is specified,
#'   the current working directory will be used.
#'
#' @export
#' @examples
#' \dontrun{
#' setwd("/somewhere") # initial working directory.
#' here() # 'here starts at /somewhere/'
#' setwd("/anywhere/else") # change working directory
#' here::u_r() # 'here starts at /anywhere/else'
#'
#' setwd("/somewhere/") # initial working directory.
#' here() # 'here starts at /somewhere/'
#' here::u_r("/anywhere/else") # 'here starts at /anywhere/else'
#' getwd() # "/anywhere/else" 
#' }
u_r <- function(target_wd=getwd()){
    detach("package:here", unload=TRUE)
    if(target_wd==getwd()){
        library(here)
    }
    setwd(target_wd)
    library(here)
}