create proper documentation for all public functions

[pmayd]

As we are moving to a proper R package for our project, I want to use document() from devtools to automatically create the documentation files that are understood by RStudio so we have proper documentation for our functions.

So we should annotate all functions like

#' Split a string
#'
#' @param x A character vector with one element.
#' @param split What to split on.
#'
#' @return A character vector.
#' @export
#'
#' @examples
#' x <- "alfa,bravo,charlie,delta"
#' strsplit1(x, split = ",")
strsplit1 <- function(x, split) {
  strsplit(x, split = split)[[1]]
}