Multi-window support (#318)

* Multi-window support

Part of the Android player is rewritten to support the multi-window mode. Now, when you turn on the multi-window mode and changing the size of the player window, the video and sound continues without breaks.

The example application is updated - support for the multi-window is added to the AndroidManifest.

* The VLCTextureView class is moved to a separate file.

* Code Formatting

* Added in the README how to set up multi-window mode in Android & v 7.1.3

* README update

Author: andyduke

flutter_vlc_player/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 7.1.3
+* Added support for multi-window mode in Android.
+Credits to Andy Chentsov (https://github.com/andyduke).
+
 ## 7.1.2
 * Add Hybrid composition support for Android.
 

flutter_vlc_player/README.md

@@ -100,6 +100,25 @@ android {
 ```proguard
 -keep class org.videolan.libvlc.** { *; }
 ```
+<hr>
+
+#### Android multi-window support
+
+To enable multi-window support in your Android application, you need to make changes to `AndroidManifest.xml`, add the `android:resizeableActivity` key for the main activity, as well as the `android.allow_multiple_resumed_activities` metadata for application:
+```xml
+<manifest ...>
+  <application ...>
+    <activity ...
+      android:resizeableActivity="true">
+      ...
+    </activity>
+    ...
+    <meta-data
+      android:name="android.allow_multiple_resumed_activities"
+      android:value="true" />
+  </application>
+</manifest>
+```
 
 <br>