git-annex sim command is working

Had to add Read instances to Key and NumCopies and some other similar
types. I only expect to use those in serializing a sim. Of course, this
risks that implementation changes break reading old data. For a sim,
that would not be a big problem.

Types/Key.hs

@@ -68,7 +68,7 @@ instance NFData KeyData
 data Key = MkKey
 	{ keyData :: KeyData
 	, keySerialization :: S.ShortByteString
-	} deriving (Show, Generic)
+	} deriving (Show, Read, Generic)
 
 instance Eq Key where
 	-- comparing the serialization would be unnecessary work