Log Message:
hs-aeson: update to 2.1.0.0.

### 2.1.0.0

- Change time instances of types with year (`Day`, `UTCTime`) to require years \ 
with at least 4 digits.
- Change `KeyValue` instances to be more general (and use equality to constraint \ 
them) instead of being more lax flexible instances.
- Export `Key` type also from `Data.Aeson.KeyMap` module.
- Export `mapWithKey` from `Data.Aeson.KeyMap` module.
- Export `ifromJSON` and `iparse` from `Data.Aeson.Types`. Add `iparseEither`.
- Add `MonadFix Parser` instance.
- Make `Semigroup Series` slightly lazier
- Add instances for `Generically` type