[ruby/rdoc] Use distinct styles for note lists and label lists

(https://github.com/ruby/rdoc/pull/1209)

* Use the original `label` description list style

As a default for all description lists, the original "label" style is
more readable.

This is slightly different from the original `label` dl though:
* slightly increased left margin for `dd` (to 1em)
* removed right margin on `dd`
* removed `dt` bottom margin and `dd` top margin, to reduce the gap
  between the term and its description (to only the standard line-height
  gap).

* Add closing tags for description list terms

Without the closing tags, the dt elements contain whitespace after the
text.  This normally isn't a big deal, but does mess some things up,
e.g: using `::after` with `content: ", "` in stylesheets.

* Restore float:left style for note lists

Unlike the original note list styles, this version sets the line-height
for all `dt` elements to be the same as the `p` elements contained
inside the `dd`, so that the second line has the same indentation as all
subsequent lines.

* Add commas between note list terms

9e69ea6d75

lib/rdoc/markup/to_html.rb

@@ -407,7 +407,7 @@ class RDoc::Markup::ToHtml < RDoc::Markup::Formatter
       "<li>"
     when :LABEL, :NOTE then
       Array(list_item.label).map do |label|
-        "<dt>#{to_html label}\n"
+        "<dt>#{to_html label}</dt>\n"
       end.join << "<dd>"
     else
       raise RDoc::Error, "Invalid list type: #{list_type.inspect}"