More tweaks to generated script docs.

- The "private interface" section is still tracked, but no longer rendered.
  We can judge the usefulness of it later and add back if there's demand.

- Documentation of event handlers was being treated the same as event
  declarations.  Now handlers are tracked separately, but not currently
  rendered in the generated doc output since usefulness is questionable.

src/parse.y

@@ -1179,7 +1179,7 @@ func_hdr:
 				   FUNC_FLAVOR_EVENT, 0, $3);
 			$$ = $3;
 			if ( generate_documentation )
-				current_reST_doc->AddEvent(
+				current_reST_doc->AddEventHandler(
 					new BroDocObj($2, reST_doc_comments));
 			}
 	|	TOK_REDEF TOK_EVENT event_id func_params