Groom text around camera up vector

Resolves #420

books/RayTracingInOneWeekend.html

@@ -2500,11 +2500,10 @@
 where we place the camera _lookfrom_, and the point we look at _lookat_. (Later, if you want, you
 could define a direction to look in instead of a point to look at.)
 
-We also need a way to specify the roll, or sideways tilt, of the camera; the rotation around the
-lookat-lookfrom axis. Another way to think about it is even if you keep `lookfrom` and `lookat`
-constant, you can still rotate your head around your nose. What we need is a way to specify an up
-vector for the camera. Notice we already we already have a plane that the up vector should be in,
-the plane orthogonal to the view direction.
+We also need a way to specify the roll, or sideways tilt, of the camera: the rotation around the
+lookat-lookfrom axis. Another way to think about it is that even if you keep `lookfrom` and `lookat`
+constant, you can still rotate your head around your nose. What we need is a way to specify an “up”
+vector for the camera. This up vector should lie in the plane orthogonal to the view direction.
 
   ![Figure [cam-look]: Camera view direction](../images/fig.cam-look.jpg)