The Highlight Callsign (13) UDP message now operates in a slightly
different way. The "Highlight last" field, when true valued, causes
all instances of the specified callsign to be highlighted in the
decoding period. This allows external applications to highlight DX
callsigns even when multiple stations are calling them. Before this
was unlikely to work since the external application would have to
respond to Decode (2) UDP messages exceedingly quickly to guarantee
successful highlighting before another decode with the same DX call
was printed. There should be no changes required to external
applications acting as servers to the WSJT-X UDP Message Protocol,
although using the version of the Highlight Callsign (13) with
"Highlight last" should not be required for adhoc callsign
highlighting. It should be reserved for commonly recurring targets and
limited to no more than 100 active highlighting requests at any one
time, otherwise there may be performance impacts on WSJT-X.
