Add decoding/encoding registries & parsers.

[ClickerMonkey]

Rekord.addDecoder('boolean', {strict: Boolean}, function(value, params) {
  if ( params.strict ) ...
  return value;
});

var Model = Rekord({
  decodings: {
    property: 'boolean(strict:true)',
  }
});

You can also pipe one decoder/encoder to another.