Specially render "styled" Markdown code blocks

Since we're already using StyledStrings for rendering Julia in the
terminal, we can also handle "styled"-labelled code blocks fancily,
thanks to the `styled` function provided by StyledStrings. In all
non-terminal contexts, the styling metadata is simply discarded, but
could be used in the future (for instance StyledStrings currently
supports HTML output too).

stdlib/Markdown/src/Markdown.jl

@@ -12,7 +12,7 @@ module Markdown
 import Base: AnnotatedString, AnnotatedIOBuffer, show, ==, with_output_color, mapany
 using Base64: stringmime
 
-using StyledStrings: StyledStrings, Face, addface!, @styled_str
+using StyledStrings: StyledStrings, Face, addface!, @styled_str, styled
 using JuliaSyntaxHighlighting: highlight, highlight!
 
 # Margin for printing in terminal.

stdlib/Markdown/src/render/html.jl

@@ -67,6 +67,9 @@ end
 
 function html(io::IO, code::Code)
     withtag(io, :pre) do
+        if code.language == "styled"
+            code = Code("", String(styled(code.code)))
+        end
         maybe_lang = !isempty(code.language) ? Any[:class=>"language-$(code.language)"] : []
         withtag(io, :code, maybe_lang...) do
             htmlesc(io, code.code)
@@ -134,6 +137,9 @@ function htmlinline(io::IO, content::Vector)
 end
 
 function htmlinline(io::IO, code::Code)
+    if code.language == "styled"
+        code = Code("", String(styled(code.code)))
+    end
     withtag(io, :code) do
         htmlesc(io, code.code)
     end

stdlib/Markdown/src/render/latex.jl

@@ -33,6 +33,9 @@ function latex(io::IO, header::Header{l}) where l
 end
 
 function latex(io::IO, code::Code)
+    if code.language == "styled"
+        code = Code("", String(styled(code.code)))
+    end
     occursin("\\end{verbatim}", code.code) && error("Cannot include \"\\end{verbatim}\" in a latex code block")
     wrapblock(io, "verbatim") do
         println(io, code.code)

stdlib/Markdown/src/render/rst.jl

@@ -26,6 +26,9 @@ function rst(io::IO, code::Code)
     elseif code.language in ("", "julia", "julia-repl")
         println(io, ".. code-block:: julia\n")
     elseif code.language == "rst"
+    elseif code.language == "styled"
+        code = Code("", String(styled(code.code)))
+        println(io, "::\n")
     else
         println(io, "::\n")
     end

stdlib/Markdown/src/render/terminal/render.jl

@@ -113,6 +113,8 @@ end
 function term(io::IO, md::Code, columns)
     code = if md.language ∈ ("", "julia", "julia-repl", "jldoctest")
         highlight(md.code)
+    elseif md.language == "styled"
+        styled(md.code)
     else
         styled"{markdown_code:$(md.code)}"
     end
@@ -185,7 +187,12 @@ function terminline(io::AnnotIO, md::Link)
 end
 
 function terminline(io::IO, code::Code)
-    print(io, styled"{markdown_inlinecode:$(code.code)}")
+    body = if code.language == "styled"
+        styled(code.code)
+    else
+        code.code
+    end
+    print(io, styled"{markdown_inlinecode:$body}")
 end
 
 function terminline(io::IO, tex::LaTeX)