Lua: allow returning a single filter from filter files

It is now possible to return a single filter from a filter file, e.g.

``` lua
-- Switch single- and double quotes
return {
  Quoted = function (q)
    elem.quotetype = elem.quotetype == 'SingleQuote'
      and 'DoubleQuote' or 'SingleQuote'
    return elem
  end
}

The filter must not contain numerical indexes, or it might be treated as
a list of filters.

1 files changed, 4 insertions, 6 deletions

diff --git a/doc/lua-filters.md b/doc/lua-filters.md
index 8b8dbfc47..0ac8a22f0 100644
--- a/doc/lua-filters.md
+++ b/doc/lua-filters.md
@@ -40,11 +40,9 @@ to small caps:
 
 ``` lua
 return {
-  {
-    Strong = function (elem)
-      return pandoc.SmallCaps(elem.content)
-    end,
-  }
+  Strong = function (elem)
+    return pandoc.SmallCaps(elem.content)
+  end,
 }
 ```
 
@@ -187,7 +185,7 @@ local filter = {
   traverse = 'topdown',
   -- ... filter functions ...
 }
-return {filter}
+return filter
 ```
 
 Support for this was added in pandoc 2.17; previous versions