The current behavior in the library is to omits if field value
would encode as empty JSON value. This behavior is different from
the bahavior in golang encoding/json which omits if field value
is an empty Go value (defined as false, 0, a nil pointer, a nil
interface value, and any empty array, slice, map, or string).
The OmitEmptyMode = 1 is added to encoding option so that cbor
would decode omitempty fields similarly to encoding/json in go.

Signed-off-by: Vu Dinh <vudinh@outlook.com>

Signed-off-by: Vu Dinh <vudinh@outlook.com>