square board and properly fit inside window

shader.h

@@ -7,3 +7,4 @@ typedef struct Shader {
 void read_shader_file(const char *path, char **buf);
 Shader create_shader(const char *vertex_path, const char *fragment_path);
 void use_shader(Shader shader);
+void set_mat4(Shader shader, const char *name, float *mat);