Began work on shotgun
Merge branch 'master' into wip

Updating this to latest master
Finished shotgun
Added projectile weapon :apply_shot_effects()

By default, this pulses the host, plays a shot sound if one has been
defined and causes screenshake if the appropriate variables have been
defined. This can be overridden if desired. It is called in
weapon:fire() (which fires a projectile).
Tweaked positional audio more
Removed debug print from Sound.lua
Added test shot sound
Reworked projectile weapon base; tweaked Weapon

Shot effects like adding heat and playing sounds are now separate from
the actual projectile firing logic. This makes it easier to override
weapon:fire(), and have the shot sound only played once for something
like a shotgun.

Also, weapons now cool even when the fire button is held.
Tweaked test shotgun
Moved shot sound to its own function

Also added pitch control to that.
Updated shotgun with separate sound call
Fixed explosions not doing damage
Added health visualisation and death explosions
Tweaked death explosions

More tweaking to come at a later point.
Tweaked test scenario
Fixed merge issues and added two shotguns