Fix apidoc macro entries

This makes various fixes to the text that is used to generate the
documentation.  The dominant change is to add the 'n' flag to indicate
that the macro takes no arguments.  A couple should have been marked
with a D (for deprecated) flag, and a couple were missing parameters,
and a couple were missing return values.

These were spotted by using Devel::PPPort on them.

1 files changed, 1 insertions, 1 deletions

diff --git a/av.h b/av.h
index 7cb63b484c..72267d6202 100644
--- a/av.h
+++ b/av.h
@@ -39,7 +39,7 @@ struct xpvav {
 /*
 =head1 Handy Values
 
-=for apidoc AmU||Nullav
+=for apidoc ADmnU||Nullav
 Null AV pointer.
 
 (deprecated - use C<(AV *)NULL> instead)