contrib: add marc21/to_marc21 liberal contrib

* BETTER Adds liberal conversion functions for MARC21, which
  allows all datafields, subfields and indicators, without
  breaking compatibility with strict MARC21.

* FIX Corrects invalid MARC21 tag in `data/authority/ad3xx.py`.

Signed-off-by: Øystein Blixhavn <oystein@blixhavn.no>

dojson/contrib/marc21/fields/ad260360.py → dojson/contrib/marc21/fields/ad25x28x.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # This file is part of DoJSON
-# Copyright (C) 2015 CERN.
+# Copyright (C) 2015, 2016 CERN.
 #
 # DoJSON is free software; you can redistribute it and/or
 # modify it under the terms of the Revised BSD License; see LICENSE
@@ -20,59 +20,28 @@
 def complex_see_reference_subject(self, key, value):
     """Complex See Reference-Subject."""
     field_map = {
+        '0': 'authority_record_control_number',
+        '8': 'field_link_and_sequence_number',
         'a': 'heading_referred_to',
         'i': 'explanatory_text',
-        '0': 'authority_record_control_number',
         '6': 'linkage',
-        '8': 'field_link_and_sequence_number',
     }
+
     order = utils.map_order(field_map, value)
 
     return {
         '__order__': tuple(order) if len(order) else None,
-        'heading_referred_to': utils.force_list(
-            value.get('a')
-        ),
         'authority_record_control_number': utils.force_list(
             value.get('0')
         ),
-        'explanatory_text': utils.force_list(
-            value.get('i')
-        ),
         'field_link_and_sequence_number': utils.force_list(
             value.get('8')
         ),
-        'linkage': value.get('6'),
-    }
-
-
-@marc21_authority.over('complex_see_also_reference_subject', '^360..')
-@utils.for_each_value
-@utils.filter_values
-def complex_see_also_reference_subject(self, key, value):
-    """Complex See Also Reference-Subject."""
-    field_map = {
-        'a': 'heading_referred_to',
-        'i': 'explanatory_text',
-        '0': 'authority_record_control_number',
-        '6': 'linkage',
-        '8': 'field_link_and_sequence_number',
-    }
-    order = utils.map_order(field_map, value)
-
-    return {
-        '__order__': tuple(order) if len(order) else None,
         'heading_referred_to': utils.force_list(
             value.get('a')
         ),
-        'authority_record_control_number': utils.force_list(
-            value.get('0')
-        ),
         'explanatory_text': utils.force_list(
             value.get('i')
         ),
-        'field_link_and_sequence_number': utils.force_list(
-            value.get('8')
-        ),
         'linkage': value.get('6'),
     }