Add my own math library

GLM works only for C++ and I plan on moving to back to C. There is
a C port, but it would be good for me to figure out vertex math myself.
Hence, my own library has been created.

graphics/rse_graphics.hpp

@@ -2,11 +2,10 @@
 #define RSE_GRAPHICS_HPP
 
 #include <cstdint>
+
+struct VulkanState;
 namespace rse::graphics
 {
-namespace vulkanbase {
-    struct VulkanState;
-};
 class RseGraphics {
     public:
     RseGraphics();
@@ -24,7 +23,7 @@ class RseGraphics {
 
     private:
     /* Hold vulkan state. It is modified by function initializing and communicating with Vulkan API */
-    vulkanbase::VulkanState* vulkan_state;
+    VulkanState* vulkan_state;
 };