Handling invalid input

[arlyon]

There are a few input values that cause panics in rand or from bad maths. It would be nice to protect users from these.

• width <= 0 cause range errors in rand
• height <= 0 cause range errors in rand
• max_samples == 0 cause divide by zero errors
• very high widths / heights or very low min_radius causes multiplication overflow errors when creating the grid vector.

The first three are easy to handle. The last one, not so much. Integer overflow is obviously not great but what if we were to fix it? Attempted allocation for > 2^64 Vec2 is a good hundred exabytes. I am for preventing an overflow panic, but I am very against handling 'too large' grids because we don't want to impose arbitrary limits.

One option is to create a proper builder, with a build method returning something along the lines of Result<BlueNoise, BuildError>.