Experimental batch crafting time reduction
Remove redundant get_batch_time function
Remove redundant instances of difficulty property

Difficulty is now loaded only by the requirements class, and is
automatically shared with constructions and recipes.
Logistic function batch crafting time reduction

A recipe can now have optional `batch_time_factors` array which
specifies maximum time reduction for a single craft as a percentage,
and a minimum batch size to reach the full time reduction.
Revert "Merge branch 'fire-from-mag-glass' of https://github.com/jcd000/Cataclysm-DDA into merge"

This reverts commit 654c3ba89f599a368df00372a3954fa759af5f75, reversing
changes made to 58cc1025ea767681a52ad688d41c8b28f25d3eeb.

Undo inattentive merge by KA101.
added ccache option for makefile, supports g++ and clang
fix for mainline builder
Merge pull request #9568 from KA101/revert

Revert "Merge branch 'fire-from-mag-glass' of https://github.com/jcd000/...
Prevent memory leak by automatically deleting the item info when the scope is left
Merge branch 'makefile_ccache' of https://github.com/DavidKeaton/Cataclysm-DDA into ccache
Merge branch 'another-memory-leak-this-time-with-windows' of https://github.com/BevapDin/Cataclysm-DDA into windel
Add diesel fuel to ammo.json.
Add diesel to ammo_types.json
Add diesel engines to var_vehicle_parts.json
Added diesel engines to vehicle_parts.json ( top level )
Added diesel fuel tanks to vehicle_parts.json ( top level )
Fix diesel fuel color
Added diesel to the fire code of field.cpp
A few recipe category fixes.
Recategorized food for more consistency.