Update render 1.14

[hollasch]

• Width 400 (× 225)
• PNG format

Ref #179

[hollasch]

The source for this image is wrong somehow. It currently contains NaNs in the output, leading to a corrupted image.

Use the progression branch to get to a debuggable state.

[trevordblack]

Hunch:
it's cause of the lack of

double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);

fmin

[hollasch]

In the progression branch, I added it (in the refract() function). No joy. Also made r_out_parallel a unit vector, but that didn't help. Added code to write out cyan for any NaN-containing color, and basically anything that touches glass gets a NaN result.