Provide a way to exclude fields from ConsoleWriter

[hach-que]

For example, you can set up ConsoleWriter in such a way that custom fields are in PartsOrder, like this:

output := zerolog.ConsoleWriter{Out: os.Stderr}
output.PartsOrder = []string{
	zerolog.TimestampFieldName,
	zerolog.LevelFieldName,
	"node",
	zerolog.MessageFieldName,
}

logger := zerolog.New(output).With().Timestamp().Str("node", node).Logger()
return &logger

However, there's no way of excluding the custom field from then being duplicated in the writeFields call. In addition, there's no way to control the rendering of custom fields in PartsOrder for e.g. adding padding for alignment.

The feature request is thus:

• Provide a way to exclude fields in the ConsoleWriter, or automatically exclude fields from writeFields if the field is specified in PartsOrder (the latter makes the most sense to me).
• ConsoleWriter.FormatFieldValue should have the field name passed to it, so that the presentation of those custom fields can be modified correctly.