Add R documentation

Contains the R base + recommended package help pages converted to HTML.

Equivalent to the fullrefman.pdf generated from source, which is also
called « The R Reference Index » on https://cran.r-project.org/manuals.html

Currently does not include reference manuals and miscellanea (FAQ, etc.)

Script building the documentation:

```bash

set -e
set -o pipefail

DEVDOCSROOT=/path/to/devdocs/docs/r

RSOURCEDIR=${TMPDIR:-/tmp}/R/latest
RBUILDDIR=${TMPDIR:-/tmp}/R/build

RLATEST=https://cran.r-project.org/src/base/R-latest.tar.gz

R="$RBUILDDIR/bin/R"
libdir="$RBUILDDIR/library"
docdir=$RBUILDDIR/doc
makevars="$RSOURCEDIR/share/make/vars.mk"

if [ ! -f "$R" ] ; then
	if [ ! -d "$RSOURCEDIR" ]; then
		mkdir -p "$RSOURCEDIR" && curl "$RLATEST" | tar -C "$RSOURCEDIR" -xzf - --strip-components=1
	fi

	[ -d "$RBUILDDIR" ] || mkdir -p "$RBUILDDIR"
	[ -f "$RBUILDDIR/config.status" ] || (cd "$RBUILDDIR" && "$RSOURCEDIR/configure")
	make -C "$RBUILDDIR" && make -C "$RBUILDDIR" docs
fi

mkdir -p "$DEVDOCSROOT/doc" && cp -r "$docdir"/* "$DEVDOCSROOT/doc/"
find "$libdir" -type d -name 'html' -printf '%P\n' | while read d; do
	mkdir -p "$DEVDOCSROOT/library/$d"
	cp -r "$libdir/$d"/* "$DEVDOCSROOT/library/$d/"
done

R_PKGS_BASE="`sed -n 's/^R_PKGS_BASE *= *//p' $makevars`"
R_PKGS_RECOMMENDED="`sed -n 's/^R_PKGS_RECOMMENDED *= *//p' $makevars`"

cat <<EOF | _R_HELP_LINKS_TO_TOPICS_=FALSE $R --vanilla --no-echo
links <- tools::findHTMLlinks()
for (pkg in c(`echo $R_PKGS_BASE $R_PKGS_RECOMMENDED | sed 's/\S\+/"&"/g;s/ /, /g'`)) {
	Rd <- tools::Rd_db(pkg, lib.loc="$libdir")
	if (!length(Rd)) {
		message(paste("ERROR: no help files found for package", pkg))
	} else {
		message(paste0(pkg, "..."))
	}
	for(f in names(Rd)) {
		out <- file.path("$DEVDOCSROOT/library", pkg, "html", sub("[Rr]d$", "html", basename(f)))
		tools::Rd2HTML(Rd[[f]], out, package = "$pkg", defines = .Platform\$OS.type,
					   outputEncoding = "UTF-8", no_links = FALSE, dynamic = FALSE,
					   Links = links, stages = c("build", "install", "render"))
	}
}
EOF

echo "DONE! Start at $DEVDOCSROOT/doc/html/index.html (or $DEVDOCSROOT/doc/html/packages.html)"
```

assets/javascripts/templates/pages/about_tmpl.coffee

@@ -676,6 +676,11 @@ credits = [
     '2012-2018 The Qt Company Ltd',
     'GFDL',
     'https://doc.qt.io/qt-5/licensing.html'
+  ], [
+    'R',
+    '1999--2012 R Foundation for Statistical Computing',
+    'GPL',
+    'https://svn.r-project.org/R/trunk/COPYING'
   ], [
     'Ramda',
     '2013-2020 Scott Sauyet and Michael Hurley',

lib/docs/filters/r/clean_html.rb

@@ -0,0 +1,34 @@
+module Docs
+  class R
+    class CleanHtmlFilter < Filter
+      def call
+        slug_parts = slug.split('/')
+        if slug_parts[0] == 'library'
+          title = at_css('h2')
+          title.inner_html = "<code>#{slug_parts[3]}</code> #{title.content}"
+
+          summary = at_css('table[summary]')
+          summary.remove if summary
+
+        elsif slug_parts[-2] == 'manual'
+          css('span[id] + h1, span[id] + h2, span[id] + h3, span[id] + h4, span[id] + h5, span[id] + h6').each do |node|
+            id = node.previous['id']
+            node.previous.remove
+            node['id'] = id.sub(/-1$/, '') if id
+          end
+          css('table.menu, div.header, hr').remove
+
+          css('.footnote h5').each do |node|
+            anchor = node.at_css('a[id]')
+            footnote = node.next_sibling
+            footnote.inner_html = "<strong>#{anchor.text}</strong>&nbsp;#{footnote.inner_html}"
+            footnote['id'] = anchor['id']
+            node.remove
+          end
+        end
+
+        doc
+      end
+    end
+  end
+end

lib/docs/filters/r/entries.rb

@@ -0,0 +1,59 @@
+module Docs
+  class R
+    class EntriesFilter < Docs::EntriesFilter
+
+      @@include_manual = false
+      @@include_misc = false
+
+      def initialize(*)
+        super
+      end
+
+      def slug_parts
+        slug.split('/')
+      end
+
+      def is_package?
+        slug_parts[0] == 'library'
+      end
+
+      def is_manual?
+        slug_parts[-2] == 'manual'
+      end
+
+      def get_name
+        return slug_parts[3] + ' − ' + at_css('h2').content if is_package?
+        title = at_css('h1.settitle')
+        title ? title.content : at_css('h1, h2').content
+      end
+
+      def get_type
+        return slug_parts[1] if is_package?
+        return at_css('h1.settitle').content if is_manual?
+        'Miscellaneous'
+      end
+
+      def include_default_entry?
+        if is_manual? or slug_parts[-1] == '00Index' or slug_parts[-1] == 'index'
+          return false
+        end
+        is_package? or self.include_misc
+      end
+
+      def additional_entries
+        return [] unless is_manual? and self.include_manual
+
+        entries = []
+        css('div.contents > ul > li').each do |node|
+          node.css('a').each do |link|
+            link_name = link.content.sub /^[0-9A-Z]+(\.[0-9]+)* /, ''
+            entries << [link_name, link['href'].split('#')[1], name]
+          end
+        end
+        return entries
+      end
+
+      private
+    end
+  end
+end

lib/docs/scrapers/r.rb

@@ -0,0 +1,31 @@
+module Docs
+  class R < FileScraper
+    self.name = 'R'
+    self.slug = 'r'
+    self.type = 'simple'
+    self.release = '4.1.0'
+    self.links = {
+      home: 'https://www.r-project.org/',
+      code: 'https://svn.r-project.org/R/'
+    }
+
+    self.root_path = 'doc/html/packages.html'
+
+    html_filters.push 'r/entries', 'r/clean_html'
+
+    options[:skip_links] = false
+
+    options[:attribution] = <<-HTML
+      Copyright (&copy;) 1999--2012 R Foundation for Statistical Computing.<br>
+      Licensed under the <a href="https://www.gnu.org/copyleft/gpl.html">GNU General Public License</a>.
+    HTML
+
+    # Never want those
+    options[:skip] = %w(
+      doc/html/packages-head-utf8.html
+      doc/html/SearchOn.html
+      doc/html/Search.html
+    )
+
+  end
+end

public/icons/docs/r/SOURCE

@@ -0,0 +1 @@
+https://svn.r-project.org/R/trunk/doc/html/Rlogo.svg