[Bleeding] Added Conversations API. Addresses BUKKIT-864

By: rmichela <deltahat@gmail.com>

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

@@ -0,0 +1,27 @@
+package org.bukkit.conversations;
+
+import java.util.regex.Pattern;
+
+/**
+ * RegexPrompt is the base class for any prompt that requires an input validated by a regular expression.
+ */
+public abstract class RegexPrompt extends ValidatingPrompt {
+
+    private Pattern pattern;
+
+    public RegexPrompt(String regex) {
+        this(Pattern.compile(regex));
+    }
+
+    public RegexPrompt(Pattern pattern) {
+        super();
+        this.pattern = pattern;
+    }
+
+    private RegexPrompt() {}
+
+    @Override
+    protected boolean isInputValid(ConversationContext context, String input) {
+        return pattern.matcher(input).matches();
+    }
+}