DOCSP-9547 whats new page (#60)

* updated whats-new page

Author: kyuan-mongodb

source/index.txt

@@ -14,6 +14,7 @@ MongoDB Java Driver
    API Documentation <http://mongodb.github.io/mongo-java-driver/4.0/apidocs/mongodb-driver-sync/index.html>
    /issues-and-help
    /compatibility
+   /whats-new
 
 Introduction
 ------------
@@ -74,3 +75,8 @@ Compatibility
 -------------
 The :doc:`Compatibility </compatibility>` section shows compatibility charts
 with JVM and MongoDB server versions.
+
+What's New
+----------
+The :doc:`What's New </whats-new>` section shows new features and
+changes in each version.

source/whats-new.txt

@@ -0,0 +1,57 @@
+==========
+What's New
+==========
+
+.. default-domain:: mongodb
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 1
+   :class: singlecol
+
+Learn what's new in:
+
+* :ref:`Version 4.2 <version-4.2>`
+* :ref:`Version 4.1 <version-4.1>`
+* :ref:`Version 4.0 <version-4.0>`
+
+
+.. _version-4.2:
+
+What's New in 4.2
+-----------------
+New features of the 4.2 Java driver release include:
+
+- Added Azure and GCP key stores to client-side field level encryption
+- Added Kerberos caching tickets for reuse in multiple authentication requests
+- Added `MongoClients <http://mongodb.github.io/mongo-java-driver/4.2/apidocs/mongodb-driver-sync/com/mongodb/client/MongoClients.html>`_ instances with ``MongoClientSettings`` or ``ConnectionString`` as the configuration
+-  The ``explain()`` method can now be used on `find <https://mongodb.github.io/mongo-java-driver/4.2/apidocs/mongodb-driver-sync/com/mongodb/client/FindIterable.html#explain()>`_ and `aggregate <https://mongodb.github.io/mongo-java-driver/4.2/apidocs/mongodb-driver-sync/com/mongodb/client/AggregateIterable.html#explain()>`_ commands
+- Added a `JsonObject <https://mongodb.github.io/mongo-java-driver/4.2/apidocs/bson/org/bson/json/JsonObject.html#%3Cinit%3E(java.lang.String)>`_ class to make encoding from and decoding to JSON more efficient by avoiding an intermediate Map representation
+- Added a `BsonRepresentation <https://mongodb.github.io/mongo-java-driver/4.2/apidocs/bson/org/bson/codecs/pojo/annotations/BsonRepresentation.html>`_ annotation that allows ``ObjectId`` BSON values to be represented as a ``String`` in `POJO <https://en.wikipedia.org/wiki/Plain_old_Java_object>`_ classes
+- Added a `Filters.empty() <https://mongodb.github.io/mongo-java-driver/4.2/apidocs/mongodb-driver-core/com/mongodb/client/model/Filters.html#empty()>`_ method
+
+.. important::
+
+   There are breaking changes that may affect your application. See the
+   `Upgrading Guide
+   <https://mongodb.github.io/mongo-java-driver/4.2/upgrading/>`_ for
+   more information.
+
+.. _version-4.1:
+
+What's New in 4.1
+-----------------
+New features of the 4.1 Java driver release include:
+
+- Significant reduction in client-perceived failover times during planned maintenance events
+- The `update() <https://mongodb.github.io/mongo-java-driver/4.1/apidocs/mongodb-driver-core/com/mongodb/client/model/UpdateOptions.html#hint(org.bson.conversions.Bson)>`_ and `delete() <https://mongodb.github.io/mongo-java-driver/4.1/apidocs/mongodb-driver-core/com/mongodb/client/model/DeleteOptions.html#hint(org.bson.conversions.Bson)>`_ methods now support index hints
+- The ``find()`` method supports `allowDiskUse() <https://mongodb.github.io/mongo-java-driver/4.1/apidocs/mongodb-driver-sync/com/mongodb/client/FindIterable.html#allowDiskUse(java.lang.Boolean)>`_ for sorts that require too much memory to execute in RAM
+- Added support for the MONGODB-AWS authentication mechanism using Amazon Web Services (AWS) Identity and Access Management (IAM) credentials
+- Authentication requires fewer round trips to the server, resulting in faster connection setup
+
+.. _version-4.0:
+
+What's New in 4.0
+-----------------
+This release adds no new features.