AsciiDoc writer: insert some needed blank lines.

Closes #1860.

src/Text/Pandoc/Writers/AsciiDoc.hs

@@ -126,7 +126,7 @@ blockToAsciiDoc :: WriterOptions -- ^ Options
 blockToAsciiDoc _ Null = return empty
 blockToAsciiDoc opts (Plain inlines) = do
   contents <- inlineListToAsciiDoc opts inlines
-  return $ contents <> cr
+  return $ contents <> blankline
 blockToAsciiDoc opts (Para [Image alt (src,'f':'i':'g':':':tit)]) = do
   blockToAsciiDoc opts (Para [Image alt (src,tit)])
 blockToAsciiDoc opts (Para inlines) = do

tests/writer.asciidoc

@@ -375,15 +375,19 @@ HTML Blocks
 Simple block on one line:
 
 foo
+
 And nested without indentation:
 
 foo
 
 bar
+
 Interpreted markdown in a table:
 
 This is _emphasized_
+
 And this is *strong*
+
 Here’s a simple block:
 
 foo
@@ -405,6 +409,7 @@ As should this:
 Now, nested:
 
 foo
+
 This should just be an HTML comment:
 
 Multiline: