====== cannon ======

Fires projectiles at creeper, bots and digitalis in range. Used by several player units.

__**Arguments**__

  ?turbo (bool)
  :If true, weapon's fire rate is increased tremendously
  ?fire_range (int)
  :Maximum distance in map pixels at which weapon will aim and fire at targets
  ?manual_mode (bool)
  :If true, cannon aims toward cursor and fires when left mouse button is clicked; if false, cannon aims and fires automatically
  ?fire_offset (Vector2)
  :The V2 offset from 0,0 on the part that the shot originates from.
  ?rotate_speed (float)
  :Maximum turn rate of cannon in degrees per frame (in manual mode cannon rotates instantly to face cursor regardless of rotate_speed)
  ?fire_cost (float)
  :Ammo consumed from parent unit per shot fired
  ?fire_delay (int)
  :Time between shots in game frames
  ?shot_speed (int)
  :Movement speed of fired shots in map pixels per frame
  ?max_age (int)
  :Time in game frames from firing until projectile despawns (a value of 0 gives projectiles unlimited lifetime)
  ?shot_damage_count (int)
  :Maximum number of creeper pixels damaged per shot
  ?shot_damage_distance (int)
  :Maximum damage radius of shots in map pixels
  ?shot_damage (int)
  :Damage to each pixel of creeper (negative values damage creeper, positive values damage anticreeper; however, there is no way to target anticreeper)per shot, in millionths (i.e. -1000000 reduces creeper depth by 1.0 in each affected pixel)
  ?shot_digitalis_damage (int)
  :Damage to each pixel of living digitalis per shot (damage is always inflicted in a 5x5 pixel square centered on the point of impact, regardless of shot_damage_count or shot_damage_distance)
  ?hit_colliders (int)
  :0 Means for the cannon shot to not hit any physics colliders. 1 or 2 specify which type pf colliders to hit. The "shothitlayer" on a part specifies which collider type a part has.
  ?hit_collider_damage (float)
  :The amount of internal health damage to do to a unit when a shot hits a collider.
  ?cannon_enabled (bool)
  :If the cannon is enabled.
  ?target_priority (int)
  :The preferred order to look for enemy targets. 0 or 1 for Creeper or Digitalis respectively.