Added support for rendering multiple lights, standardized shaders to use snake case for variables and camel case for functions, stubbed PBR material shader include.

assets/shaders/include/material_struct.glsl

@@ -0,0 +1,16 @@
+struct Material {
+  vec3 color;
+  vec3 roughness;
+  vec3 metalic;
+  vec3 specular;
+
+  bool use_color_texture;
+  bool use_roughness_texture;
+  bool use_metalic_texture;
+  bool use_specular_texture;
+
+  sampler2D color_tex;
+  sampler2D roughness_tex;
+  sampler2D metalic_tex;
+  sampler2D specular_tex;
+};