Sections and subsections support

[maksymiuks]

Apparently NEWS files could also be provided to the package as .Rd files (see ?utils::news). This forces us to consider another class of tags, which are section and subsection that could be nested. It means we can no longer hard code level in with_md_title to be 2L as this will depend on depth we are currently on

rd2markdown/R/rd2markdown.R

Lines 160 to 165 in b448cb8

	rd2markdown.description <- function(x, fragments = c(), ..., title = NULL) {
	out <- map_rd2markdown(x, ..., collapse = "")
	out <- gsub("\n{1,}$", "", out)
	out <- gsub("\n*\\\\lifecycle\\{(.*)\\}\n*", "\n\nLifecycle: *\\1*\n\n", out)
	with_md_title(out, title, 2L, ...)
	}

Each section tag should increment the level of all tags nested in it while keeping its own level. I'll try to prepare a draft for this change and how I see it.