Added serializer for metrics record rn_citation_data field (#19)

* Values supported include timestamp and hastable/dict

* Added serializer metrics records rn_citation_data is an array of hashtables.  protobuf serializer converts them into a list of citation_record objects.

adsmsg/metrics_record.py

@@ -4,7 +4,23 @@
 class MetricsRecord(Msg):
 
     def __init__(self, *args, **kwargs):
-        super(MetricsRecord, self).__init__(metrics_pb2.MetricsRecord(), args, kwargs)
+        """construct protobuf metrics record, ususally from a database dict
+        
+        value for rn_citation_data needs speical processing 
+          to clearly specify its contents for protobuf. example data: 
+          [{"ref_norm": 0.2, "pubyear": 1954, "auth_norm": 0.25, "bibcode": "1954PhRv...93..257G", "cityear": 1954}, ...]
+        the citation_records message defines the contents of the json object 
+        """
+        instance = metrics_pb2.MetricsRecord()
+        kwargs.pop('id', None)  # local database key field is not serialized
+        rn_citation_data = kwargs.pop('rn_citation_data', None)
+        super(MetricsRecord, self).__init__(instance, args, kwargs)
+        if rn_citation_data:
+            for current in rn_citation_data:
+                citation_record = instance.rn_citation_data.add()
+                for key in current:
+                    setattr(citation_record, key, current[key])
+
 
 
 class MetricsRecordList(Msg):