Ornamented logical values

[tranma]

The efficient representation of values make it difficult to write safe operations naturally, so we end up with functions like these:

ppValue :: Schema.Column -> Logical.Value -> Either JsonLogicalEncodeError Aeson.Value

I think @jystic has investigated a GADT encoding of values before. That plus some conversion to the existing ADT, à la Ghostbuster or Ornaments, should give us the best of both worlds.

[tranma]

A side benefit is, with the ornamented approach, the effort to introduce a GADT encoding will be incremental, so we need not convert the entire library to use it at once.