Implement zip_register_progress_callback().

This function can be used to provide user interface updates
during zip_close().
diff --git a/NEWS.md b/NEWS.md
index 0555595..7b50aaa 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -6,6 +6,7 @@
 * Fix seeking in zip_source_file if start > 0.
 * Add zip_fseek() for seeking in uncompressed data.
 * Add zip_ftell() for telling position in uncompressed data.
+* Add zip_register_progress_callback() for UI updates during zip_close()
 
 1.1.3 [2016-05-28]
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