Release notes for alternate graphic 880 fields

Signed-off-by: Dan Scott <dan@coffeecode.net>

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+Display alternate graphic (880) fields
+======================================
+
+By default, Evergreen displays alternate graphic fields, if any, for
+contributors (1xx / 7xx), titles (245), edition statements (250), imprints
+(260), notes (5xx), and subjects (6xx) in search results and record details
+per the Library of Congress MARC21 specifications:
+
+* http://www.loc.gov/marc/bibliographic/bd880.html
+* http://www.loc.gov/marc/bibliographic/ecbdcntf.html
+* http://www.loc.gov/marc/bibliographic/ecbdmulti.html (Model A)
+
+Default display
+---------------
+In general, alternate graphic fields display below the corresponding
+primary field. One exception is the attribution summary on the record details
+page, in which the alternate graphic field contents display between the
+primary field content and the attribution statement. To support CSS
+customizations, HTML elements for the graphic fields have the class attribute
+value `graphic880`.
+
+Implementation details
+----------------------
+The template file `parts/misc_util.tt2` defines two macros for retrieving
+linked 880 fields:
+
+* `get_graphic_880s`: given a _target_field_ scalar value representing a MARC
+  field tag, populate the _graphic_880s_ list with hashes containing the
+  target field tag and any graphic fields linked to that particular tag, with
+  the values for each being a simple concatenation of all subfields that are
+  not control subfields (per
+  http://www.loc.gov/marc/bibliographic/ecbdcntf.html). The structure of the
+  `graphic_880s` list is as follows:
++
+------------------------------------------------------------------------
+[
+    {
+        "primary": {"occur": 01, "value": "foo foo"},
+        "graphic": [
+            {
+                "occur": 01,
+                "value": "bar bar",
+                "orient": "rtl",
+                "script": "CJK"
+            }
+        ]
+    }
+]
+------------------------------------------------------------------------
+* `get_linked_880s` macro iterates over the content of the `linked_fields`
+  list, in which each element of the list to be a scalar representing the $6
+  control subfield link info. The macro populates the `graphics` list with a
+  set of graphic field hashes with the following structure:
++
+------------------------------------------------------------------------
+[
+    {
+        "occur": 01,
+        "value": "bar bar",
+        "orient": "rtl",
+        "script": "CJK"
+    }
+]
+------------------------------------------------------------------------
+
+`misc_util.tt2` preserves legacy attribute lists to enable previous TPAC
+customizations to continue to function normally.