Update 'Works in progress'

Works-in-progress.md

@@ -41,6 +41,7 @@
     - [ ] `flat_tree`
     - [ ] UTF-8 `string` (See BigJ's string)
         - [ ] UTF-8 range identification function
+    - [ ] CBOR parser and serializer
     - [ ] `tuple`
     - Filesystems
         - [ ] `generic_filesystem` type erasing wrapper (`gp::function` style?)