Support timestamp-micros in AvroSerDe

This change only supports timestamp-millis. Avro 1.8.2 also supports timestamp-micros. https://avro.apache.org/docs/1.8.2/spec.html#Timestamp+%28microsecond+precision%29

timestamp-micros should also be supported in hive AvroSerde because hive timestamps support nano second level precision.

https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Types#LanguageManualTypes-TimestampstimestampTimestamps

One possibility is to support avro timestamp-millis and avro timestamp-micros in serialization. Avro Deserializer can map hive timestamp to timestamp-micros.