With data-client added as library module (#3656)

* With data-client added as library module

* Fix build

data-client/README.md

@@ -0,0 +1,101 @@
+# Wikimedia Android data client
+An Android library for communicating with Wikimedia projects, with Rx bindings and other utilities.
+
+## Motivation and philosophy
+
+Here are the purposes for creating this library:
+
+* Encapsulate the various model structures that are returned by MediaWiki APIs,
+as well as by REST APIs provided by Wikimedia services.
+
+* Provide high-level bindings for Retrofit and RxJava for executing calls to MediaWiki APIs to
+further simplify client integration, while also allowing customization and extension.
+
+* Provide numerous common utility methods, so that they don't need to be duplicated.
+
+## Integration with your app
+
+Add the dependency to your Gradle file as usual:
+
+```
+implementation "com.dmitrybrant:wikimedia-android-data-client:0.0.18"
+```
+
+The only nontrivial point of integration with the library is the `AppAdapter` class:  You
+need to create a class that inherits from `AppAdapter` and implement its methods.  The
+methods are mostly self-explanatory, and deal with user account management, cookie storage,
+and a few other customizations.
+
+Once you create this class (suppose it's called `MyAppAdapter`), you should pass it into
+the `AppAdapter` singleton when your app starts:
+
+```
+@Override
+public void onCreate() {
+    ...
+    AppAdapter.set(new MyAppAdapter());
+    ...
+}
+```
+
+## Making calls to APIs
+
+Notice that there is an interface called `Service` that contains a number of API definitions
+for talking with a MediaWiki server. To use any of the functions in the interface, you should
+use the `ServiceFactory` class. For example:
+
+```
+WikiSite wiki = new WikiSite("en.wikipedia.org");
+
+Observable observable = ServiceFactory.get(wiki).fullTextSearch("foo");
+```
+
+That's it! Notice that most of the API calls return an `Observable` response which you can
+feed into an Rx subscription.
+
+Note: the `ServiceFactory` class contains automatic caching logic, so that multiple calls to
+`get()` the service for the same `WikiSite` will be very efficient.
+
+## Custom API calls
+
+The `ServiceFactory` class also allows you to provide a service interface with custom
+API functions. Suppose you create your own service interface that looks like this:
+
+```
+public interface MyInterface {
+
+    @GET("action=myawesomeaction")
+    Observable<MyAwesomeResponse> myAwesomeApiCall(@Query("parameter1") parameter);
+
+}
+```
+
+You can then use it with `ServiceFactory` this way:
+
+```
+WikiSite wiki = new WikiSite("my.awesome.wiki");
+
+Observable observable = ServiceFactory.get(wiki, "https://my.awesome.wiki/", MyInterface.class)
+        .myAwesomeApiCall("foo");
+```
+
+## Utility methods
+
+The library contains a potpourri of utility methods found under the `util` package. Feel free
+to browse through them and use them as necessary.
+
+## License
+
+Copyright 2019 Wikimedia Foundation
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.