type based git config handling

Now there's a Config type, that's extracted from the git config at startup.
Note that laziness means that individual config values are only looked up
and parsed on demand, and so we get implicit memoization for all of them.
So this is not only prettier and more type safe, it optimises several
places that didn't have explicit memoization before. As well as getting rid
of the ugly explicit memoization code.

Not yet done for annex.<remote>.* configuration settings.

Command/Unused.hs

@@ -22,7 +22,6 @@ import Logs.Unused
 import Annex.Content
 import Utility.FileMode
 import Logs.Location
-import Config
 import qualified Annex
 import qualified Git
 import qualified Git.Command
@@ -181,11 +180,9 @@ exclude smaller larger = S.toList $ remove larger $ S.fromList smaller
  - so will easily fit on even my lowest memory systems.
  -}
 bloomCapacity :: Annex Int
-bloomCapacity = fromMaybe 500000 . readish
-	<$> getConfig (annexConfig "bloomcapacity") ""
+bloomCapacity = fromMaybe 500000 . annexBloomCapacity <$> Annex.getConfig
 bloomAccuracy :: Annex Int
-bloomAccuracy = fromMaybe 1000 . readish
-	<$> getConfig (annexConfig "bloomaccuracy") ""
+bloomAccuracy = fromMaybe 1000 . annexBloomAccuracy <$> Annex.getConfig
 bloomBitsHashes :: Annex (Int, Int)
 bloomBitsHashes = do
 	capacity <- bloomCapacity