Use MetaInlines not MetaBlocks for multimarkdown metadata fields.

This gives better results in converting to e.g. pandoc markdown.

Ref: <https://groups.google.com/d/msgid/pandoc-discuss/9728d1f4-040e-4392-aa04-148f648a8dfdn%40googlegroups.com>

src/Text/Pandoc/Readers/Markdown.hs

@@ -298,7 +298,7 @@ kvPair allowEmpty = try $ do
           (try $ newline >> lookAhead (blankline <|> nonspaceChar))
   guard $ allowEmpty || not (T.null val)
   let key' = T.concat $ T.words $ T.toLower key
-  let val' = MetaBlocks $ B.toList $ B.plain $ B.text val
+  let val' = MetaInlines $ B.toList $ B.text val
   return (key',val')
 
 parseMarkdown :: PandocMonad m => MarkdownParser m Pandoc

test/command/mmd-metadata.md

@@ -0,0 +1,20 @@
+```
+% pandoc -f markdown_mmd -t markdown -s
+Title: Blah blah blah
+Author: Doo de Doo
+Base Header Level: 1
+Bibliography: Pubs.bib
+Lang: en-GB
+
+body
+^D
+---
+author: Doo de Doo
+baseheaderlevel: 1
+bibliography: Pubs.bib
+lang: en-GB
+title: Blah blah blah
+---
+
+body
+```