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