Update nut to 15.8.

Update nut to 15.8.
Based on PR#43776 by Kamel Derouiche for 15.7.

What's new in nut 15.8:
 * This release updates the USDA database to include some data corrections for
   milk.
 * The program's initial data load is now considerably faster.

What's new in nut 15.7:
 * This version includes an improvement to the automatic calorie tool to make it
   better able to hold fat mass or lean mass constant.
 * Also, there is now a facility to explicitly set the ratio between linoleic
   and alpha-linolenic acids.

What's new in nut 15.0:
 * This release introduces the new USDA Nutrient Database SR22 and allows
   current nut installations to have their existing meal records reinterpreted
   with the new database.

What's new in nut 14.5a:
 * The new feature "Weight Log Regression" does not tell you what you weigh;
   what it does is apply linear regression to a series of daily weight and body
   fat percentage entries to smooth out the random noise and tell you which
   direction your weight is trending, how fast it is going there, and how much
   of the change is lean or fat.