Squirrel: Fix inaccessible class member variables, improvements (#3031)

Fixes a bug in simplesquirrel, which caused exposed class member variables to be inaccessible from Squirrel.

Additionally:

* Simplesquirrel now supports custom getters and setters for class member variables. Because of this, more `get_` and `set_` functions of objects now have an alternative variable, which can also be used.
* All `get_` and `set_` functions which were made obsolete by member variables are now un-deprecated, because of a noticeable preference amongst scripters to keep both options available for convenience.

src/object/candle.cpp

@@ -157,6 +157,8 @@ Candle::register_class(ssq::VM& vm)
   cls.addFunc("puff_smoke", &Candle::puff_smoke);
   cls.addFunc("get_burning", &Candle::get_burning);
   cls.addFunc("set_burning", &Candle::set_burning);
+
+  cls.addVar("burning", &Candle::get_burning, &Candle::set_burning);
 }
 
 /* EOF */

src/object/candle.hpp

@@ -67,6 +67,10 @@ class Candle final : public MovingSprite
   void set_burning(bool burning);
 
 private:
+  /**
+   * @scripting
+   * @description The burning state of the candle.
+   */
   bool burning; /**< true if candle is currently lighted */
   bool flicker; /**< true if candle light is to flicker */
   Color lightcolor; /**< determines color or light given off */

src/object/conveyor_belt.cpp

@@ -172,6 +172,12 @@ ConveyorBelt::set_speed(float target_speed)
   m_speed = target_speed;
 }
 
+float
+ConveyorBelt::get_speed() const
+{
+  return m_speed;
+}
+
 
 void
 ConveyorBelt::register_class(ssq::VM& vm)
@@ -183,6 +189,9 @@ ConveyorBelt::register_class(ssq::VM& vm)
   cls.addFunc("move_left", &ConveyorBelt::move_left);
   cls.addFunc("move_right", &ConveyorBelt::move_right);
   cls.addFunc("set_speed", &ConveyorBelt::set_speed);
+  cls.addFunc("get_speed", &ConveyorBelt::get_speed);
+
+  cls.addVar("speed", &ConveyorBelt::get_speed, &ConveyorBelt::set_speed);
 }
 
 /* EOF */

src/object/conveyor_belt.hpp

@@ -58,30 +58,35 @@ class ConveyorBelt final : public MovingSprite
   /** @name Scriptable Methods */
   /**
    * @scripting
-   * Starts the conveyor belt.
+   * @description Starts the conveyor belt.
    */
   void start();
   /**
    * @scripting
-   * Stops the conveyor belt.
+   * @description Stops the conveyor belt.
    */
   void stop();
   /**
    * @scripting
-   * Makes the conveyor shift objects to the left.
+   * @description Makes the conveyor shift objects to the left.
    */
   void move_left();
   /**
    * @scripting
-   * Makes the conveyor shift objects to the right.
+   * @description Makes the conveyor shift objects to the right.
    */
   void move_right();
   /**
    * @scripting
-   * Change the shifting speed of the conveyor.
+   * @description Change the shifting speed of the conveyor.
    * @param float $target_speed
    */
   void set_speed(float target_speed);
+  /**
+   * @scripting
+   * @description Returns the shifting speed of the conveyor.
+   */
+  float get_speed() const;
 
 private:
   void update_hitbox() override;
@@ -90,6 +95,10 @@ class ConveyorBelt final : public MovingSprite
   bool m_running;
   Direction m_dir;
   int m_length;
+  /**
+   * @scripting
+   * @description The shifting speed of the conveyor.
+   */
   float m_speed;
 
   float m_frame;