Common

• Fix: Added fmin to book text for cos_theta of refract (#732)
• Fix: Standardized naming for ray-t and time parameters (#746)
• Fix: random_unit_vector() was incorrect (#697)
• Fix: Synchronize text and copies of hittable.h
• Fix: Synchronize copies of hittable_list.h, material.h, sphere.h
• Change: refactor sphere::hit() method to reuse common blocks of code.
• Change: Improved the explanation and calculation of sphere UV coordinates (#533)

In One Weekend

• Fix: Catch cases where lambertian::scatter() yields degenerate scatter rays (#619)
• Fix: Syntax error in listing 58 (Dielectric material class with reflection) (#768)
• Fix: Correct wording for ray traversal text (#766)
• Change: Wrote brief explanation waving away negative t values in initial normal sphere

The Next Week

• Fix: Catch cases where lambertian::scatter() yields degenerate scatter rays (#619)

The Rest of Your Life

• Fix: Missing override keyword for xz_rect::pdf_value() and xz_rect::random() methods (#748)
• Fix: Synchronize book and source for cornell_box() function.
• Fix: Introduction of light code was introduced out of sequence (#738, #740)
• Fix: ray_color() was creating a new light for every ray bounce (#759)