Make chronological and recentFirst to respect metadata

My stab at #111 (and a first Haskell code contribution)

---
```haskell
chronological, recentFirst :: MonadMetadata m => [Item a] -> m [Item a]
```

Doesn't look like a possible type as `getItemUTC` explictly returns `Compiler` and ghc complains about it

```
src/Hakyll/Web/Template/List.hs:64:17:
    Could not deduce (m ~ Compiler)
    from the context (MonadMetadata m)
      bound by the type signature for
                 chronological :: MonadMetadata m => [Item a] -> m [Item a]
```