stream encoding improvements for PLAINTEXT recording

[brutzman]

Need several stream encoding improvements for PLAINTEXT recording:

• Better treatment of time values to indicate HH:MM:SS.dd
• Corresponding COMMENT PDU for optional real-time clock synchronization
• Consider a commented key in the log indicating variable names upon first appearance of each PDU type

https://github.com/open-dis/open-dis7-java/blob/master/src/edu/nps/moves/dis7/utilities/stream/PduRecorderSelfTestENCODING_PLAINTEXT_PduCaptureLog.dislog

[brutzman]

# Clock Time reference value (perhaps from Simulation Management PDU)
#  6.2.14 Clock Time record

Time measurements that surpass 1 h shall be represented by a Clock Time record. The fields of this record
are as follows:
a) Hours. This field shall specify the hours since 0000 h 1 January 1970 UTC. This field shall be
represented by a 32-bit integer.
b) Time Past the Hour. This field shall specify the time past the hour indicated in the Hour field. This
field shall be represented by a Timestamp (see 6.2.88)

# 1278.1, section 6.2.88 Timestamp
# Preferable time representations:
59:55.765432 absolute [human readable]
59,55.765432,absolute [CSV]

is there another standard? several; we might prefer XML Schema xsd:time format for consistency with DIS ENCODING_XML