fix endless recursion in creature::symbol_color
add game::critter_at to get any kind of critter
use critter_at during projectile_attack
restack inventory and remove invlet from original worn item
restack inventory after showing inventory_item_menu from adv. inv.
fix typo

Fixes http://smf.cataclysmdda.com/index.php?topic=5336.0 .
rewrote inventory::assign_empty_invlet to re-use an existing hotkey in case it is forced to assign a valid hotkey
Merge pull request #6099 from KA101/typofix

fix typo
Merge pull request #6091 from BevapDin/target-npcs-2

Allow shooting npcs
Merge pull request #6092 from BevapDin/fix-worn-invlet-bug

Fix worn invlet bug
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into more_death
Fixed the noncompiling github version.