Add star_get_lhs_names

[ChandlerLutz]

star_get_lhs_names <- function(star) {
  ## Assume that the lhs vars are right below the "Dependent variable" line
  dep.var.row <- which(grepl("Dependent variable", x = star))
  col.numbers.row <- star[c(dep.var.row + 3)]
  if (!grepl("\\(1\\)", col.numbers.row)) 
    stop("Error: `star_get_lhs_names` only works on a default stargazer regression latex table")
  
  lhs.vars <- star[c(dep.var.row + 2)] %>%
    gsub("\\\\\\\\", "", x = .) %>%
    sub("\\[-1.8ex\\]", "", x = .) %>%
    strsplit(x = ., "&") %>%
    unlist(.) %>%
    stringr::str_trim() %>%
    .[2:length(.)]

  if (length(lhs.vars) != (star_ncol(star) - 1))
    stop("Error: In `star_get_lhs_names`, the length of the LHS variables is not equal to `1 - star_ncol(star)`. Are you sure you are passing a default stargazer latex regression table to `star_get_lhs_names`")

  return(lhs.vars)

}