[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

paper-api/src/main/java/org/bukkit/conversations/ConversationCanceller.java

@@ -0,0 +1,29 @@
+package org.bukkit.conversations;
+
+/**
+ * A ConversationCanceller is a class that cancels an active {@link Conversation}. A Conversation can have more
+ * than one ConversationCanceller.
+ */
+public interface ConversationCanceller extends Cloneable {
+
+    /**
+     * Sets the conversation this ConversationCanceller can optionally cancel.
+     * @param conversation A conversation.
+     */
+    public void setConversation(Conversation conversation);
+
+    /**
+     * Cancels a conversation based on user input/
+     * @param context Context information about the conversation.
+     * @param input The input text from the user.
+     * @return True to cancel the conversation, False otherwise.
+     */
+    public boolean cancelBasedOnInput(ConversationContext context, String input);
+
+    /**
+     * Allows the {@link ConversationFactory} to duplicate this ConversationCanceller when creating a new {@link Conversation}.
+     * Implementing this method should reset any internal object state.
+     * @return A clone.
+     */
+    public ConversationCanceller clone();
+}