wip(plot): region layout, hot handles and draggable handles (build restored)

include/plot/plot.hpp

@@ -53,6 +53,7 @@
 #include <plot/plot/legend.hpp>
 #include <plot/plot/measure.hpp>
 #include <plot/plot/plot.hpp>
+#include <plot/plot/region.hpp>
 #include <plot/plot/ticks.hpp>
 #include <plot/plot/trace.hpp>