Rewrite armor damage absorption code
Rewrite armour damage code
Added chitin as a material
set up JSON for materials
Added more materials calls, moved material resistance matrix to json
use materials functions in armour absorption code
Fixed material not being passed correctly, and added chitin to item factory
separate out materials contributions to armour protection values
One can now choose to ignore further sound interruptions and complete current task. Example: reloading while dozens of zeds are beating down walls.
Reduce difficulty to smash a shrub into underbrush.
outer layers of armour protect inner layers
Rework learning mechanics, following issue #613

Implements items 1 through 5, from issue #613.
Fully separate armour geometry from materials
Added a new function and UI to re-layer clothing
Added American Flag Spawn for School
Added American Flag
Added GET_FLAG
Added Find Flag
Added find flag dialogue
Advanced inventory will now sort via the 's' key: unsorted (order that
items were added), by name, weight, volume, and charges. (pending more).
Also:
* up/down in the 'e'xamine window will move to the next / previous
item in the list.
* weight and volume are displayed for ground / car squares