ENH gereralize amount lookup function

dhall/Types.dhall

@@ -404,7 +404,7 @@ let EntryNumGetter =
     ConstN: a constant value
     AmountN: the value of the 'Amount' column
     -}
-      < LookupN : Text | ConstN : Double | AmountN | NegAmountN >
+      < LookupN : Text | ConstN : Double | AmountN : Double >
 
 let EntryTextGetter =
     {-

lib/Internal/Utils.hs

@@ -346,10 +346,7 @@ resolveValue :: TxRecord -> EntryNumGetter -> InsertExcept Double
 resolveValue TxRecord {trOther, trAmount} s = case s of
   (LookupN t) -> readDouble =<< lookupErr SplitValField t trOther
   (ConstN c) -> return c
-  AmountN -> return a
-  NegAmountN -> return $ negate a
-  where
-    a = fromRational trAmount
+  AmountN m -> return $ (* m) $ fromRational trAmount
 
 resolveAcnt :: TxRecord -> SplitAcnt -> InsertExcept T.Text
 resolveAcnt = resolveSplitField AcntField