Implemented custom duplicate key handling

- Supports: throw an exception (by default), ignore, overwrite & merge into a JSONArray
 - With tests, 4/4 passed.

src/main/java/org/json/JSONParserConfiguration.java

@@ -4,23 +4,47 @@ package org.json;
  * Configuration object for the JSON parser. The configuration is immutable.
  */
 public class JSONParserConfiguration extends ParserConfiguration {
+    /**
+     * The way should be used to handle duplicate keys.
+     */
+    private JSONDuplicateKeyStrategy duplicateKeyStrategy;
 
-  /**
-   * Configuration with the default values.
-   */
-  public JSONParserConfiguration() {
-    super();
-  }
+    /**
+     * Configuration with the default values.
+     */
+    public JSONParserConfiguration() {
+        this(JSONDuplicateKeyStrategy.THROW_EXCEPTION);
+    }
 
-  @Override
-  protected JSONParserConfiguration clone() {
-    return new JSONParserConfiguration();
-  }
+    /**
+     * Configure the parser with {@link JSONDuplicateKeyStrategy}.
+     *
+     * @param duplicateKeyStrategy Indicate which way should be used to handle duplicate keys.
+     */
+    public JSONParserConfiguration(JSONDuplicateKeyStrategy duplicateKeyStrategy) {
+        super();
+        this.duplicateKeyStrategy = duplicateKeyStrategy;
+    }
 
-  @SuppressWarnings("unchecked")
-  @Override
-  public JSONParserConfiguration withMaxNestingDepth(final int maxNestingDepth) {
-    return super.withMaxNestingDepth(maxNestingDepth);
-  }
+    @Override
+    protected JSONParserConfiguration clone() {
+        return new JSONParserConfiguration();
+    }
 
+    @SuppressWarnings("unchecked")
+    @Override
+    public JSONParserConfiguration withMaxNestingDepth(final int maxNestingDepth) {
+        return super.withMaxNestingDepth(maxNestingDepth);
+    }
+
+    public JSONParserConfiguration withDuplicateKeyStrategy(final JSONDuplicateKeyStrategy duplicateKeyStrategy) {
+        JSONParserConfiguration newConfig = this.clone();
+        newConfig.duplicateKeyStrategy = duplicateKeyStrategy;
+
+        return newConfig;
+    }
+
+    public JSONDuplicateKeyStrategy getDuplicateKeyStrategy() {
+        return this.duplicateKeyStrategy;
+    }
 }