add focus to camera position.

js/pixl/public/trixl.html

		gl.uniform4f(program.color, -1, -1, -1, -1);
		trixl.pos = {x: 0, y: 0, z: 5, a: 0};
		trixl.focus = {x: 0, y: 0, z: 5, a: 0};
		var angle = {x: 0, y: 0, z: 0};
		var offset = {x: 0, y: 0, z: 0};
			);
			var camera_pos = camera.slice(12, 15);
			var focus_pos = mat4.multiplyMany(
				matrix.translate(trixl.pos.x, trixl.pos.y, trixl.pos.z + 5),
				matrix.rotateY(trixl.pos.a)
				matrix.translate(trixl.pos.x + trixl.focus.x, trixl.pos.y + trixl.focus.y, trixl.pos.z + trixl.focus.z),
				matrix.rotateY(trixl.pos.a + trixl.focus.a)
			).slice(12, 15);
			var up = [0, 1, 0];
			camera = mat4.lookAt([], camera_pos, focus_pos, up);