Add methods to set and reset max health. Adds BUKKIT-266

By: feildmaster <admin@feildmaster.com>

paper-api/src/main/java/org/bukkit/entity/Damageable.java

@@ -0,0 +1,59 @@
+package org.bukkit.entity;
+
+/**
+ * Represents an {@link Entity} that has health and can take damage.
+ */
+public interface Damageable extends Entity {
+    /**
+     * Deals the given amount of damage to this entity.
+     *
+     * @param amount Amount of damage to deal
+     */
+    void damage(int amount);
+
+    /**
+     * Deals the given amount of damage to this entity, from a specified entity.
+     *
+     * @param amount Amount of damage to deal
+     * @param source Entity which to attribute this damage from
+     */
+    void damage(int amount, Entity source);
+
+    /**
+     * Gets the entity's health from 0 to {@link #getMaxHealth()}, where 0 is dead.
+     *
+     * @return Health represented from 0 to max
+     */
+    int getHealth();
+
+    /**
+     * Sets the entity's health from 0 to {@link #getMaxHealth()}, where 0 is dead.
+     *
+     * @param health New health represented from 0 to max
+     * @throws IllegalArgumentException Thrown if the health is < 0 or > {@link #getMaxHealth()}
+     */
+    void setHealth(int health);
+
+    /**
+     * Gets the maximum health this entity has.
+     *
+     * @return Maximum health
+     */
+    int getMaxHealth();
+
+    /**
+     * Sets the maximum health this entity can have.
+     * <p />
+     * If the health of the entity is above the value provided it will be set to that value.
+     * <p />
+     * Note: An entity with a health bar ({@link Player}, {@link EnderDragon}, {@link Wither}, etc...} will have their bar scaled accordingly.
+     *
+     * @param health amount of health to set the maximum to
+     */
+    void setMaxHealth(int health);
+
+    /**
+     * Resets the max health to the original amount.
+     */
+    void resetMaxHealth();
+}