Create orthographic projection function

linear_alg.h

@@ -86,6 +86,7 @@ float vec4_dot(vec4_t v, vec4_t u);
 mat4_t mat4_mul(mat4_t m, mat4_t n);
 mat4_t mat4_lookat(vec3_t camera, vec3_t target, vec3_t up);
 mat4_t mat4_perspective(float aspect, float fov, float near, float far);
+mat4_t mat4_orthographic(float width, float height, float near, float far);
 mat4_t mat4_translate_vec3(vec3_t v);
 mat4_t mat4_scale_vec3(vec3_t v);
 mat4_t mat4_rotate_quaternion(vec4_t q);