Alow prefixing log output with a timestamp.

Alow prefixing log output with a timestamp.

When AppTimestampLog is set to 1 all output to stdout and stderr will be
prefixed with a millisecond-precision ISO8601 timestamp.

Timestamp prefixing implies online rotation mode.  It should be
considered experimental as it requires splitting input lines by LF with
no way of knowing for certain that the input stream actually is
line-based.

Thanks Nicolas Ducrocq.