Reworks acid protection code, Works the same except now takes body_parts_covered flags into account and is overall a neater piece of code.
Items worn INSIDE armour only melt when that armour is melted, Backpacks, Belts and handheld items are all worn externally so melt regardless of armour
Also updates pixel_x and pixel_y randomisation of grey goo.
Fixes more span classes. Replaces some "for() show_message()" with "visible_message()". Adding a suicide message for slimes. Fixes simple_animal/corgi having two attackby procs.
Fixes adjustmask verb for sechailer letting you chose the user mob from a list of all mobs on screen.
Merge branch 'master' of https://github.com/tgstation/-tg-station into SpanFix1

Conflicts:
	code/modules/mob/living/simple_animal/friendly/corgi.dm
Merge pull request #6182 from phil235/AdjustMaskFix

Fixes adjustmask verb for sechailer
Merge pull request #6127 from phil235/SpanFix1

Fixes span classes and show_message()'s
Merge pull request #6105 from RemieRichards/AcidProtectionUpdate

Acid protection update