Add backends

- Renamed GfxOpenGL to GfxOPenGL2
- Added GfxOpenGL3 backend for OpenGL 3.3+
- Added WIP DirectX9 backend
- Added structure for Citro3D
- Added linear Allocator

source/common.cpp

@@ -1,6 +1,6 @@
 #include <iostream>
 #include <pd/common.hpp>
 
-void PD::Log(const std::string& txt) {
+PD_API void PD::Log(const std::string& txt) {
   std::cout << "[PD] " << txt << std::endl;
 }