Added support for Date and List form params (#202).

src/main/java/org/gitlab4j/api/GitLabApiForm.java

 package org.gitlab4j.api;
 
+import java.util.Date;
+import java.util.List;
+
 import javax.ws.rs.core.Form;
 import javax.ws.rs.core.MultivaluedHashMap;
 
+import org.gitlab4j.api.utils.ISO8601;
+
 /**
  * This class extends the standard JAX-RS Form class to make it fluent.
  */
@@ -27,10 +32,75 @@ public class GitLabApiForm extends Form {
         return (withParam(name, value, false));
     }
 
+    /**
+     * Fluent method for adding Date query and form parameters to a get() or post() call.
+     *
+     * @param name the name of the field/attribute to add
+     * @param date the value of the field/attribute to add
+     * @return this GitLabAPiForm instance
+     */
+    public GitLabApiForm withParam(String name, Date date) throws IllegalArgumentException {
+        return (withParam(name, date, false));
+    }
+
+    /**
+     * Fluent method for adding Date query and form parameters to a get() or post() call.
+     *
+     * @param name the name of the field/attribute to add
+     * @param date the value of the field/attribute to add
+     * @param required the field is required flag
+     * @return this GitLabAPiForm instance
+     * @throws IllegalArgumentException if a required parameter is null or empty
+     */
+    public GitLabApiForm withParam(String name, Date date, boolean required) throws IllegalArgumentException {
+        return (withParam(name, (date == null ? null : ISO8601.toString(date)), required));
+    }
+
+    /**
+     * Fluent method for adding a List type query and form parameters to a get() or post() call.
+     *
+     * @param <T> the type contained by the List
+     * @param name the name of the field/attribute to add
+     * @param values a List containing the values of the field/attribute to add
+     * @return this GitLabAPiForm instance
+     */
+    public <T> GitLabApiForm withParam(String name, List<T> values) {
+        return (withParam(name, values, false));
+    }
+
+    /**
+     * Fluent method for adding a List type query and form parameters to a get() or post() call.
+     *
+     * @param <T> the type contained by the List
+     * @param name the name of the field/attribute to add
+     * @param values a List containing the values of the field/attribute to add
+     * @param required the field is required flag
+     * @return this GitLabAPiForm instance
+     * @throws IllegalArgumentException if a required parameter is null or empty
+     */
+    public <T> GitLabApiForm withParam(String name, List<T> values, boolean required) throws IllegalArgumentException {
+
+        if (values == null || values.isEmpty()) {
+            if (required) {
+                throw new IllegalArgumentException(name + " cannot be empty or null");
+            }
+
+            return (this);
+        }
+
+        for (T value : values) {
+            if (value != null) {
+                this.param(name + "[]", value.toString());
+            }
+        }
+
+        return (this);
+    }
+
     /**
      * Fluent method for adding query and form parameters to a get() or post() call.
      * If required is true and value is null, will throw an IllegalArgumentException.
-     * 
+     *
      * @param name the name of the field/attribute to add
      * @param value the value of the field/attribute to add
      * @param required the field is required flag
@@ -40,7 +110,6 @@ public class GitLabApiForm extends Form {
     public GitLabApiForm withParam(String name, Object value, boolean required) throws IllegalArgumentException {
 
         if (value == null) {
-
             if (required) {
                 throw new IllegalArgumentException(name + " cannot be empty or null");
             }