Added IMGUI_DISABLE_DEMO_WINDOWS support (#603)

Unlike ImGui only ShowDemoWindow of the public implot.h api is actually defined in implot_demo.cpp.

Refrained from moving ShowStyleEditor, ShowStyleSelector, ShowUserGuide, ShowMetricsWindow to implot_demo.cpp like ImGui.

Author: StewMcc

implot_demo.cpp

@@ -44,6 +44,8 @@
 
 #define CHECKBOX_FLAG(flags, flag) ImGui::CheckboxFlags(#flag, (unsigned int*)&flags, flag)
 
+#if !defined(IMGUI_DISABLE_DEMO_WINDOWS)
+
 // Encapsulates examples for customizing ImPlot.
 namespace MyImPlot {
 
@@ -2479,4 +2481,10 @@ void PlotCandlestick(const char* label_id, const double* xs, const double* opens
 
 } // namespace MyImplot
 
+#else
+
+void ImPlot::ShowDemoWindow(bool* p_open) {}
+
+#endif
+
 #endif // #ifndef IMGUI_DISABLE