convert GitRepo to struct with constructor

Locations.hs

@@ -0,0 +1,18 @@
+{- git-annex file locations
+ -}
+
+module Locations where
+
+import GitRepo
+
+{- An annexed file's content is stored somewhere under .git/annex/ -}
+annexDir :: GitRepo -> String -> IO FilePath
+annexDir repo key = do
+	dir <- gitDir repo
+	return $ dir ++ "/annex/" ++ key
+
+{- Long-term state is stored in files inside the .git-annex directory
+ - in the git repository. -}
+stateLoc = ".git-annex"
+gitStateDir :: GitRepo -> FilePath
+gitStateDir repo = (top repo) ++ "/" ++ stateLoc ++ "/"