rscb: Access and Load SCB Data through API

#' Cached ssd database
#'
#' A data.frame containing condensed information on all directories,
#' subdirectories, and tables in the "ssd" database at SCB \url{www.scb.se}. ssd
#' is the main database for national statistics, and, currently, the only one
#' accessible through the API.
#'
#' When compiled in March 2019, the highest level directory had information on:
#' \itemize{\item Labour market \item Population \item Housing, construction,
#' and building \item Energy \item Financial markets \item Trade in goods and
#' services \item Household finances \item Agriculture, forestry, and fishery
#' \item Living conditions \item Democracy \item Environment \item National
#' accounts \item Business activities \item Public finances \item Prices and
#' consumption \item Transport and communications \item Education and research}
#'
#' The cache is created by running \code{\link{scb_create_cache}}, which
#' recursively calls \code{\link{scb_list}}. For each directory, the ID path and
#' text description is stored. For tables, in addition to the ID path and text
#' description, the variables, values, and date range present in the table is
#' also stored.
#'
#' In a future iteration of this table, the intention is to flatten the
#' structure to store tables on the same rows as their directories. It will also
#' include a new column containing information on when the table as last
#' updated.
#'
#' @format A data frame with approximately 2800 rows and 10 columns: \describe{
#'   \item{id}{ID path to use to query directory or table} \item{depth}{1 =
#'   highest level directory in cache, incremented for each subdirectory}
#'   \item{type}{l for directory, t for table} \item{name}{Name of directory /
#'   table} \item{updated}{Last time table was updated}
#'   \item{var_desc}{Variables present in table} \item{val_desc}{Values present
#'   in table} \item{date_start}{Oldest entry in table} \item{date_end}{Most
#'   recent entry in table} }
#' @source \url{www.scb.se} via API through \code{\link{scb_create_cache}}
"scb_cache"