- Rename \<thing>_case:nnn to \<thing>_case:nnF and introduce
   \<thing>_case:nn, \<thing>_case:nnT and \<thing>_case:nnTF
 - Add concept of key groups to l3keys, allowing selective setting
   of keys with the same 'path'
 - Remove .code:x and .meta:x key properties
 - Internal changes to seq and prop structures, allowing faster
   \prop_map_inline:Nn
-- 
Joseph Wright