Add ParseTimeFromNum function for timezone support.

[qiuyesuifeng]

see #19 and #20
ParseTimeFromNum function not consider timezone, when convert to timestamp type, time validity check does not work well.

we should check following tests later.

    table := []struct {
        Input                int64
        ExpectDateTimeError  bool
        ExpectDateTimeValue  string
        ExpectTimeStampError bool
        ExpectTimeStampValue string
        ExpectDateError      bool
        ExpectDateValue      string
    }{
        {700101000000, false, "1970-01-01 00:00:00", false, "1970-01-01 00:00:00", false, "1970-01-01"},
        {380119031407, false, "2038-01-19 03:14:07", false, "2038-01-19 03:14:07", false, "2038-01-19"},
       }