Now have more test for the base functionality but need to push render tests and find a way to test the GUI. I've also brought in sol2 for lua integration but not sure what to do with it.

panel.cpp

@@ -1,4 +1,5 @@
 #include "panel.hpp"
+#include "dbc.hpp"
 
 void Panel::resize(int w, int h) {
   $dirty = true;
@@ -13,6 +14,7 @@ void Panel::set_renderer(Component renderer) {
 }
 
 void Panel::add(Component child) {
+  dbc::pre("must set_renderer first", $component != nullptr);
   $dirty = true;
   $component->Add(child);
 }