allow custom element separators in sugar logger model

[chatter1986]

By default, consoleEncoder add '\t' to separator elements, can provide customization capabilities？

func (c consoleEncoder) EncodeEntry(ent Entry, fields []Field) (*buffer.Buffer, error) {
	line := bufferpool.Get()
        
        ...

	for i := range arr.elems {
		if i > 0 {
			line.AppendByte('\t')
		}
		fmt.Fprint(line, arr.elems[i])
	}

func (c consoleEncoder) addTabIfNecessary(line *buffer.Buffer) {
	if line.Len() > 0 {
		line.AppendByte('\t')
	}
}

[prashantv]

There's a pending change, see #697 which aims to provide this feature, but it has some pending code review comments.