Generalize ability system

Make effects usable outside the context of abilities.

(These changes bring breaking changes for the Ability API)

Fixes #115

litiengine/src/main/java/de/gurkenlabs/litiengine/abilities/effects/AbilityEffect.java

@@ -0,0 +1,33 @@
+package de.gurkenlabs.litiengine.abilities.effects;
+
+import de.gurkenlabs.litiengine.abilities.Ability;
+import de.gurkenlabs.litiengine.abilities.targeting.TargetingStrategy;
+
+/**
+ * The `AbilityEffect` class is an abstract class that represents an effect
+ * associated with a specific ability. It extends the `Effect` class and is
+ * used to apply effects that are tied to a particular ability.
+ * <p>
+ * This class provides a way to manage and access the ability that triggers the effect,
+ * allowing for the integration of ability-specific attributes such as the executor and duration.
+ */
+public abstract class AbilityEffect extends Effect {
+  private final Ability ability;
+
+  /**
+   * Constructs a new `AbilityEffect` with the specified targeting strategy and ability.
+   * <p>
+   * The effect will inherit the executor and duration attributes from the provided ability.
+   *
+   * @param targetingStrategy The strategy used to select the targets for this effect.
+   * @param ability           The ability associated with this effect, providing information such as the executor and duration.
+   */
+  protected AbilityEffect(TargetingStrategy targetingStrategy, Ability ability) {
+    super(targetingStrategy, ability.getExecutor(), ability.getAttributes().duration().get());
+    this.ability = ability;
+  }
+
+  public Ability getAbility() {
+    return ability;
+  }
+}

litiengine/src/main/java/de/gurkenlabs/litiengine/abilities/effects/AttributeEffect.java

@@ -1,13 +1,13 @@
 package de.gurkenlabs.litiengine.abilities.effects;
 
-import de.gurkenlabs.litiengine.abilities.Ability;
+import de.gurkenlabs.litiengine.abilities.targeting.TargetingStrategy;
 import de.gurkenlabs.litiengine.attributes.Attribute;
 import de.gurkenlabs.litiengine.attributes.AttributeModifier;
 import de.gurkenlabs.litiengine.attributes.Modification;
 import de.gurkenlabs.litiengine.entities.ICombatEntity;
 
 /**
- * An attribute effect appies an attribute modifier to the affected entity when applied and removes it when ceased.
+ * An attribute effect applies an attribute modifier to the affected entity when applied and removes it when ceased.
  *
  * @param <T>
  *          the generic type
@@ -17,12 +17,17 @@ public abstract class AttributeEffect<T extends Number> extends Effect {
   /** The modifier. */
   private final AttributeModifier<T> modifier;
 
-  protected AttributeEffect(
-      final Ability ability,
+  protected AttributeEffect(final TargetingStrategy targetingStrategy,
+                            final Modification modification,
+                            final double delta) {
+    this(targetingStrategy, null, modification, delta);
+  }
+
+  protected AttributeEffect(final TargetingStrategy targetingStrategy,
+      final ICombatEntity executingEntity,
       final Modification modification,
-      final double delta,
-      final EffectTarget... targets) {
-    super(ability, targets);
+      final double delta) {
+    super(targetingStrategy, executingEntity);
     this.modifier = new AttributeModifier<>(modification, delta);
   }