Progression 3 updates

Use math markup in captions for book 3. Book 2 already does this.

Remove unnecessary includes

Move setprecision call for consistency. This keeps the call in the same
location across multiple versions of pi.cc.

Update Listing 3.03 with change highlighting

Update Listing 3.04, 3.06, 3.12, 3.14, 3.15, 3.17, 3.18, 3.22, 3.24,
3.26

Clean up listing 3.07 pi.cc alternate version one

Update Listing 3.08 and following text

Update listing 3.13 Explicit uniform PDF for x^2

Update listing 3.16
  - Add missing includes
  - Add precise decimal value of expected result

Fix equation text in section 8.2

Update listing 3.28; code is broken at this point

This fixes the lack of `material::scatter()` signature change in the
`material` base class, but still lacks the corresponding changes
required in metal, dielectric, diffuse_light and isotropic materials. In
addition, it lacks the change required to the `camera::ray_color()`
function call to `material::scatter()`.

sphere_plot.cc: Fix iteration count

Resolves #1018
Resolves #1312

Author: hollasch