ConTeXt writer: Use setupcaption to separate style from content.

Instead of adding 'nunumber' every time we place a figure...

Closes #1067.

data/templates

@@ -1 +1 @@
-Subproject commit 4bdebc73b0b2025cf01704e7e564088c34d8f86c
+Subproject commit 8cadd4f2044c0c25842eeb5a2370a6e3384f4bd4

src/Text/Pandoc/Writers/ConTeXt.hs

@@ -130,7 +130,7 @@ blockToConTeXt (Plain lst) = inlineListToConTeXt lst
 -- title beginning with fig: indicates that the image is a figure
 blockToConTeXt (Para [Image txt (src,'f':'i':'g':':':_)]) = do
   capt <- inlineListToConTeXt txt
-  return $ blankline $$ "\\placefigure[here,nonumber]" <> braces capt <>
+  return $ blankline $$ "\\placefigure[here]" <> braces capt <>
            braces ("\\externalfigure" <> brackets (text src)) <> blankline
 blockToConTeXt (Para lst) = do
   contents <- inlineListToConTeXt lst

tests/writer.context

@@ -30,6 +30,8 @@
 \setupitemize[autointro]    % prevent orphan list intro
 \setupitemize[indentnext=no]
 
+\setupcaption[figure][number=no]  % don't number figures
+
 \setupthinrules[width=15em] % width of horizontal rules
 
 \setupdelimitedtext
@@ -842,7 +844,7 @@ or here: <http://example.com/>
 
 From \quotation{Voyage dans la Lune} by Georges Melies (1902):
 
-\placefigure[here,nonumber]{lalune}{\externalfigure[lalune.jpg]}
+\placefigure[here]{lalune}{\externalfigure[lalune.jpg]}
 
 Here is a movie {\externalfigure[movie.jpg]} icon.