Make placement of bibliography possible with reference-section-title

[cderv]

This is a documented way in Pandoc: https://pandoc.org/MANUAL.html#placement-of-the-bibliography
To add in index.Rmd

reference-section-title: Awesome biblio

but it does not seems to work.

Error in vapply(idx2, character(1), FUN = function(i) head(nms[idx > i],  : 
  values must be length 1,
 but FUN(X[[7]]) result is length 0

Issue is here:

bookdown/R/html.R

Lines 367 to 373 in b66380e

	h1 = grep('^<div (id="[^"]+" )?class="section level1("| )', html_body)
	h2 = grep('^<div (id="[^"]+" )?class="section level2("| )', html_body)
	idx2 = if (split_level == 1) h1 else if (split_level == 2) sort(c(h1, h2))
	n = length(idx2)
	nms_chaps = if (length(idx)) {
	vapply(idx2, character(1), FUN = function(i) head(nms[idx > i], 1))
	}

I believe there will be one more title in HTML not expected by bookdown because not in files as it will be inserted by Pandoc itself