Merge branch 'mh/notes-string-list'

Improve the asymptotic performance of the cat_sort_uniq notes merge
strategy.

* mh/notes-string-list:
  string_list_add_refs_from_colon_sep(): use string_list_split()
  notes: fix handling of colon-separated values
  combine_notes_cat_sort_uniq(): sort and dedup lines all at once
  Initialize sort_uniq_list using named constant
  string_list: add a function string_list_remove_empty_items()

Documentation/technical/api-string-list.txt

@@ -38,7 +38,8 @@ member (you need this if you add things later) and you should set the
   `unsorted_string_list_delete_item`.
 
 . Can remove items not matching a criterion from a sorted or unsorted
-  list using `filter_string_list`.
+  list using `filter_string_list`, or remove empty strings using
+  `string_list_remove_empty_items`.
 
 . Finally it should free the list using `string_list_clear`.
 
@@ -75,6 +76,12 @@ Functions
 	to be deleted.  Preserve the order of the items that are
 	retained.
 
+`string_list_remove_empty_items`::
+
+	Remove any empty strings from the list.  If free_util is true,
+	call free() on the util members of any items that have to be
+	deleted.  Preserve the order of the items that are retained.
+
 `string_list_longest_prefix`::
 
 	Return the longest string within a string_list that is a