Improve codecs

[calvinlfer]

Divide codecs into 3 parts:

1. Primitive Encoders and Decoders (as per documentation). Primitives include UdtValue and materialization of any type A that can be derived using 2
2. User-Defined Types Encoders and Decoders which derive from 1 (note the mutual induction which is necessary to provide valid instances for 3 since you cannot have Rows nested within Rows but you can have UdtValues nested in Rows)
3. Row Decoders and a Row Component Encoder which also derive from 1

This separation allows us to eliminate writing down derive when it comes to codecs for any structure (be it a Row or a UdtValue).

Special-casing optimizations have been done on Primitive codecs in order to avoid using the generic get or set method whenever possible which results in a lookup to the internal driver codec registry.

For example:

Add coverage + coveralls integration into the builds

Improve error messages giving users the opportunity to see exactly what went wrong via DecoderException and the structure that failed to decode.

For example:

implicit val eitherPersonDecoder = CqlRowDecoder[Person].either
cql"SELECT * FROM persons"
  .query[Either[codecs.DecoderException, Person]]
  .execute
  .tap {
    case Left(d: DecoderException) =>
      putStrLn(s"DecoderException: ${d.debug}")
​
    case _ =>
      UIO.unit
   }

Improve compositionality of codecs