Move camera initialisation into seperate module

include/camera.h

@@ -0,0 +1,17 @@
+#ifndef CAMERA_H
+#define CAMERA_H
+
+#include "vec3.h"
+
+#include <stdint.h>
+
+typedef struct {
+	vec3_t pos;
+	vec3_t pix_origin, x_step, y_step;
+} camera_t;
+
+camera_t camera_init(
+    vec3_t pos, double focal_len, double viewport_height, uint32_t img_width,
+    uint32_t img_height);
+
+#endif