Docx writer: support --number-sections.

Closes #1413.

MANUAL.txt

@@ -982,7 +982,7 @@ header when requesting a document from a URL:
 
 `-N`, `--number-sections`
 
-:   Number section headings in LaTeX, ConTeXt, HTML, or EPUB output.
+:   Number section headings in LaTeX, ConTeXt, HTML, Docx, or EPUB output.
     By default, sections are not numbered.  Sections with class
     `unnumbered` will never be numbered, even if `--number-sections`
     is specified.
@@ -1125,6 +1125,7 @@ header when requesting a document from a URL:
         - Verbatim Char
         - Footnote Reference
         - Hyperlink
+        - Section Number
 
         Table style:
 

data/docx/word/styles.xml

@@ -414,6 +414,10 @@
       <w:sz w:val="22" />
     </w:rPr>
   </w:style>
+  <w:style w:type="character" w:customStyle="1" w:styleId="SectionNumber">
+    <w:name w:val="Section Number" />
+    <w:basedOn w:val="BodyTextChar" />
+  </w:style>
   <w:style w:type="character" w:styleId="FootnoteReference">
     <w:name w:val="Footnote Reference" />
     <w:basedOn w:val="BodyTextChar" />

src/Text/Pandoc/Writers/Docx.hs

@@ -210,8 +210,11 @@ writeDocx :: (PandocMonad m)
           => WriterOptions  -- ^ Writer options
           -> Pandoc         -- ^ Document to convert
           -> m BL.ByteString
-writeDocx opts doc@(Pandoc meta _) = do
-  let doc' = walk fixDisplayMath doc
+writeDocx opts doc = do
+  let Pandoc meta blocks = walk fixDisplayMath doc
+  let blocks' = makeSections True Nothing blocks
+  let doc' = Pandoc meta blocks'
+
   username <- P.lookupEnv "USERNAME"
   utctime <- P.getCurrentTime
   oldUserDataDir <- P.getUserDataDir
@@ -898,11 +901,21 @@ blockToOpenXML' opts (Div (ident,_classes,kvs) bs) = do
   header <- dirmod $ stylemod $ blocksToOpenXML opts hs
   contents <- dirmod $ bibmod $ stylemod $ blocksToOpenXML opts bs'
   wrapBookmark ident $ header <> contents
-blockToOpenXML' opts (Header lev (ident,_,_) lst) = do
+blockToOpenXML' opts (Header lev (ident,_,kvs) lst) = do
   setFirstPara
   paraProps <- withParaPropM (pStyleM (fromString $ "Heading "++show lev)) $
                     getParaProps False
-  contents <- inlinesToOpenXML opts lst
+  number <-
+        if writerNumberSections opts
+           then
+             case lookup "number" kvs of
+                Just n -> do
+                   num <- withTextPropM (rStyleM "SectionNumber")
+                            (inlineToOpenXML opts (Str n))
+                   return $ num ++ [mknode "w:r" [] [mknode "w:tab" [] ()]]
+                Nothing -> return []
+           else return []
+  contents <- (number ++) <$> inlinesToOpenXML opts lst
   if T.null ident
      then return [mknode "w:p" [] (paraProps ++ contents)]
      else do