message: Improve naming of function kinds
diff: type_type : kind.
  % Functions
  - function_type : kind -> kind -> kind. % Kinds to Kinds, eg. `Type -> (Format -> Format)`
  - function_type : type' -> kind -> kind. % Types to Kinds, eg. `Int -> (Type -> Type)`
  - function_type : kind -> type' -> kind. % Kinds to Types, eg. `(A : Type) -> Array 3 A`
  + function_kind : kind -> kind -> kind. % Kinds to Kinds, eg. `Type -> (Format -> Format)`
  + function_kind : type' -> kind -> kind. % Types to Kinds, eg. `Int -> (Type -> Type)`
  + function_kind : kind -> type' -> kind. % Kinds to Types, eg. `(A : Type) -> Array 3 A`
  function_type : type' -> type' -> type'. % Types to Types, eg. `(n : Int) -> Array n Int`
  function_intro_type : type' -> type'. % Types parameterised by types, eg. `fun A => Array 3 A`
  function_intro_term : type' -> type'. % Types parameterised by terms, eg. `fun n => Array n U32Be`
  