Update book 1 following progression walkthrough

These are changes to fix or clarify the book 1 text based on a full
walkthrough of all the code changes. This includes the following
changes:

- Text clarifications.
- Added clarification that run examples are based on Windows + CMake.
- Fixed erroneous partial listing of first PPM image data.
- Clarified troubleshooting text for first image generation.
- Changed first image to be a pure red/green gradient, dropping blue
  from 0.25 to 0 for clarity.
- Added hint that the first scanline progress output will likely be too
  fast to notice on early simple renders.
- Fixed many code listing blank line issues.
- Fixed many code change highlighting mistakes.
- Fixed a few code listing errors.
- Generally added more context to code changes, as a lot of listings of
  new code lacked any context.
- Fixed cases where required code changes were missing.
- Fixed vec3 functions with missing `inline` specifiers.
- Fixed accidental re-use of "dielectric" label for four separate code
  listings.

Author: hollasch