relax alphabetic numbering consecutive requirements slightly to allow, eg, 3 followed by 3b

dlibrary/dlibrary.py

@@ -784,7 +784,7 @@ def alphabetic_numbering(entries, start_point):
     indices = list(alphabetized.keys())
     indices.sort()
     for i in range(1, len(indices)):
-        if indices[i][0] - indices[i-1][0] != 1:
+        if not (indices[i][0] - indices[i-1][0] == 1 or (indices[i-1][0] == 0 and indices[i][0] == 2)):
             debug(f'Adjacent indices {indices[i][0]} and {indices[i-1][0]} are not consecutive, giving up')
             return None
     return alphabetized