feat(plot): per-trace legend with measured layout and swatches

include/plot/plot.hpp

@@ -50,6 +50,7 @@
 #include <plot/plot/axis.hpp>
 #include <plot/plot/cursor.hpp>
 #include <plot/plot/grid.hpp>
+#include <plot/plot/legend.hpp>
 #include <plot/plot/measure.hpp>
 #include <plot/plot/plot.hpp>
 #include <plot/plot/ticks.hpp>