Add missing documentation about rustybeer HOT 5 CLOSED

Ok, I'll have a go at writing some documentation

from rustybeer.

What's the difference between calculators::boil_off and calculators::diluting, other than that calculators::diluting is missing a method to calculate a new volume? While writing the documentation I noticed they seemed identical

from rustybeer.

Very valid point. I can't see a difference myself. @drodil chime in?

from rustybeer.

Actually they don't have any difference. Diluting is adding more water to the batch to reach desired gravity (water amount goes up so gravity goes down) while boil-off is to remove water (water amount goes down so gravity goes up). So when doing boil-off, this calculator should return negative number indicating how much water should be removed by boiling. See a reference calculator here https://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/

from rustybeer.

I'm not 100% sure I follow, but if I understand correctly, we can just get rid of calculators::boil_off::BoilOff, and instead use calculators::diluting::Diluting::calculate_new_volume (I think is the correct method), and just negate, allowing us to remove calculators::boil_off::BoilOff?

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