Added the concept of a projectile.

By: sunkid <sunkid@iminurnetz.com>

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

@@ -0,0 +1,23 @@
+package org.bukkit.entity;
+
+/**
+ * Represents a shootable entity
+ */
+public interface Projectile extends Entity {
+
+    /**
+     * Retrieve the shooter of this projectile. The returned value can be null
+     * for projectiles shot from a {@link Dispenser} for example.
+     *
+     * @return the {@link LivingEntity} that shot this projectile
+     */
+    public LivingEntity getShooter();
+
+    /**
+     * Set the shooter of this projectile
+     *
+     * @param shooter
+     *            the {@link LivingEntity} that shot this projectile
+     */
+    public void setShooter(LivingEntity shooter);
+}