fix attrs for implicit figures

the syntax `![caption](path){.class}` (when interpreted as an implicit
figure) attaches `class` to the `<img>` tag. this moves it to the
`<figure>`

langfilter/Main.hs

@@ -25,7 +25,8 @@ main = toJSONFilter filter where
     defColor <- getDefColor m
     let ?lang = lang
     let ?defColor = defColor
-    fmap (walk makeEbnf .
+    fmap (walk fixFigureClass .
+          walk makeEbnf .
           walk makeQuotes .
           walk (concatMap makeBlocks) .
           walk inlineLetterList) $
@@ -51,6 +52,11 @@ pluck1 []     _  = Nothing
 pluck1 (x:xs) ys = (x,) <$> pluck x ys <|> pluck1 xs ys
 
 
+fixFigureClass :: Block -> Block
+fixFigureClass (Figure (_, c1, a1) cap [Plain [Image (i, c2, a2) alt path]]) =
+  Figure (i, c1 ++ c2, a1 ++ a2) cap [Plain [Image ("", [], []) alt path]]
+fixFigureClass b = b
+
 makeBlocks :: Block -> [Block]
 makeBlocks (Div ("", clss, []) blks)
   | Just (cls, rest) <- pluck1 ["figure", "aside"] clss =