Add markdown figure filters.

markdown-figures/Makefile

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+.PHONY: test
+
+test:

markdown-figures/README.md

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+# Support for figures in Markdown
+
+This filter provides two syntaxs to represent figures in markdown.
+
+## Explicit syntax
+
+The explicit syntax is constructed using a `div` with "figure" class. The
+caption is also specified using a `div` but with a "caption" class.
+
+Here is an example.
+
+```
+::: { .figure }
+
+content.
+
+:::: {.caption }
+caption
+::::
+
+:::
+```
+
+All elements inside the figure that are an image without a caption in its own
+paragraph become html's `img` tags.
+
+Here is an example of figure containing two images and a caption.
+
+```{markdown}
+::: { .figure }
+
+![](test/media/rId25.jpg "")
+
+![](test/media/rId25.jpg "")
+
+:::: {.caption }
+caption
+::::
+
+:::
+```
+
+This will result in a single figure containing multiple images.
+
+```
+$ pandoc -f markdown -t native --lua-filter=md-figure-explicit.lua fig-explicit.md
+
+[Figure ("",[],[]) (Caption (Just []) [Para [Str "caption"]])
+	[ Plain [Image ("",[],[]) [] ("test/media/rId25.jpg","")]
+	, Plain [Image ("",[],[]) [] ("test/media/rId25.jpg","")]]]
+```
+
+
+```{html}
+<figure>
+<img src="test/media/rId25.jpg" />
+<img src="test/media/rId25.jpg" />
+<figcaption><p>caption</p></figcaption>
+</figure>
+```
+
+This will result in a single figure containing multiple images.
+
+## Implicit syntax
+
+The second syntax uses the last paragraph inside the figure as the caption.
+
+```{markdown}
+::: { .figure }
+
+
+![](test/media/rId25.jpg "")
+
+![](test/media/rId25.jpg "")
+
+This is a caption with
+multiple lines
+
+:::
+
+```
+
+This results in the following output:
+
+
+```
+$ pandoc -f markdown -t native --lua-filter=md-figure-implicit.lua fig-implict.md
+[Figure ("",[],[])
+	(Caption
+		(Just [])
+		[ Para [Str "This",Space,Str "is",Space,Str "a",Space,Str "caption",Space,Str "with",SoftBreak,Str "multiple",Space,Str "lines"]]) 
+	[Plain [Image ("",[],[]) [] ("test/media/rId25.jpg","")],Plain [Image ("",[],[]) [] ("test/media/rId25.jpg","")]]]
+```
+
+```{html}
+<figure>
+<img src="test/media/rId25.jpg" />
+<img src="test/media/rId25.jpg" />
+<figcaption><p>This is a caption with multiple lines</p></figcaption>
+</figure>
+```
+
+## Sample Firefox's HTML rendering
+
+For the implicit syntax example, this is firefox's render.
+
+![Example](render.png)

markdown-figures/md-figure-explicit.lua

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+--- Translate Divs with the "figure" class into Figure elements.
+-- The contents of last child Div with the "caption" class will be used as the
+-- figure caption.
+function Div(div)
+
+  local content = div.content
+  local attr = div.attr
+  local null_caption = {
+    short = {},
+    long = {}
+  }
+
+  if attr.classes:includes "figure" then
+
+    local new_content =  pandoc.List({})
+
+    -- A div with the caption class is captured as the figure's
+    -- caption.
+    for _,elem in pairs(div.content) do
+      if elem.t == 'Div' then
+        null_caption.long = elem.content
+      else
+        new_content:insert(elem)
+      end
+    end
+
+
+    -- Remove the figure for `SimpleFigure` with no caption inside a Figure.
+    local final_content = pandoc.List({})
+
+    for _,elem in pairs(new_content) do
+      -- Check that it is a simple figure with no caption
+      if elem.t == 'Para' and 
+        #elem.content == 1 and
+        elem.content[1].t == 'Image' and
+        #elem.content[1].caption == 0 then
+
+        local image = elem.content[1]
+        final_content:insert(pandoc.Plain({image}))
+      else
+        final_content:insert(elem)
+      end
+    end
+
+    -- Remove the figure class in the output
+    attr.classes = attr.classes:filter(
+    function(c) return c ~= "figure" end)
+
+    return pandoc.Figure(final_content, null_caption, attr)
+  end
+
+  -- Return an identical div when it lacks the "figure" class.
+  return pandoc.Div(content, attr)
+end

markdown-figures/md-figure-implicit.lua

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+--- Translate Divs with the "figure" class into Figure elements.
+-- The contents of last paragraph became the figure caption will be used as the
+-- figure caption.
+function Div(div)
+
+  local content = div.content
+  local attr = div.attr
+  local null_caption = {
+    short = {},
+    long = {}
+  }
+
+  if attr.classes:includes "figure" then
+
+    local new_content =  pandoc.List({})
+
+    -- Capture the last element
+    local last_elem = nil
+
+    for _,elem in pairs(div.content) do
+      if last_elem then
+        new_content:insert(last_elem)
+      end
+      last_elem = elem
+    end
+
+    -- If the last element is a paragraph, use it as caption.
+    if last_elem then
+      if last_elem.t == 'Para' then
+        null_caption.long = { last_elem }
+      else
+        new_content:insert(last_elem)
+      end
+    end
+
+    -- Remove the figure for `SimpleFigure` with no caption inside a Figure.
+    local final_content = pandoc.List({})
+
+    for _,elem in pairs(new_content) do
+      -- Check that it is a simple figure with no caption
+      if elem.t == 'Para' and 
+        #elem.content == 1 and
+        elem.content[1].t == 'Image' and
+        #elem.content[1].caption == 0 then
+
+        local image = elem.content[1]
+        final_content:insert(pandoc.Plain({image}))
+      else
+        final_content:insert(elem)
+      end
+    end
+
+    -- Remove the figure class in the output
+    attr.classes = attr.classes:filter(
+      function(c) return c ~= "figure" end)
+
+    return pandoc.Figure(final_content, null_caption, attr)
+  end
+
+  -- Return an identical div when it lacks the "figure" class.
+  return pandoc.Div(content, attr)
+end