#14 Add EventTimeStamp decoding

[Steve Karg]

The RPM demo chokes on the following property (event time stamp) – see below.

Derek traced the code down from:

Read_Property_Multiple_Ack_Handler ()
                rpm_ack_decode_service_request ()
                               bacapp_decode_context_data ()
                                               value->tag = bacapp_context_tag_type(property, tag_number);

Looking at the bacapp_context_tag_type() it does not have a case to handle the PROP_EVENT_TIME_STAMPS

BACnetTimeStamp ::= CHOICE {
    time [0] Time, -- this form was deprecated in version 1 revision 21
    sequence-number [1] Unsigned (0..65535),
    datetime [2] BACnetDateTime
}