expose the new directory capability stuff

src/Tahoe/Directory.hs

 module Tahoe.Directory (
     module Tahoe.Directory.Internal.Parsing,
     module Tahoe.Directory.Internal.Types,
+    module Tahoe.Directory.Internal.Capability,
 ) where
 
+import Tahoe.Directory.Internal.Capability (
+    ConfidentialShowable (..),
+    DirectoryCapability (..),
+    pReadCHK,
+    pVerifyCHK,
+ )
 import Tahoe.Directory.Internal.Parsing (parse, serialize)
 import Tahoe.Directory.Internal.Types (Directory (..), Entry (..))