Add --contains flag to abcfield.py. Currently we rely on any N: field with a Change: subnotice being the first N: field. Add --contains field to abcfield.py to remove this restriction. Also use it to extract new subfield Credit: and add that if present to the tune information in print and on web.

--- a/web/css/dottes.css	Sun Aug 04 21:28:05 2013 +0100
+++ b/web/css/dottes.css	Sun Aug 04 22:09:25 2013 +0100
@@ -244,3 +244,12 @@
 div.dottes-change-link
 {
 }
+
+div.dottes-credit-no
+{
+    display: none;
+}
+
+div.dottes-credit-yes
+{
+}