turn Raylib-cs.Android into android library

Raylib-cs.Android.Sample/Resources/AboutResources.txt

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+Images, layout descriptions, binary blobs and string dictionaries can be included 
+in your application as resource files.  Various Android APIs are designed to 
+operate on the resource IDs instead of dealing with images, strings or binary blobs 
+directly.
+
+For example, a sample Android app that contains a user interface layout (main.xml),
+an internationalization string table (strings.xml) and some icons (drawable-XXX/icon.png) 
+would keep its resources in the "Resources" directory of the application:
+
+Resources/
+    drawable/
+        icon.png
+
+    layout/
+        main.xml
+
+    values/
+        strings.xml
+
+In order to get the build system to recognize Android resources, set the build action to
+"AndroidResource".  The native Android APIs do not operate directly with filenames, but 
+instead operate on resource IDs.  When you compile an Android application that uses resources, 
+the build system will package the resources for distribution and generate a class called "Resource" 
+(this is an Android convention) that contains the tokens for each one of the resources 
+included. For example, for the above Resources layout, this is what the Resource class would expose:
+
+public class Resource {
+    public class Drawable {
+        public const int icon = 0x123;
+    }
+
+    public class Layout {
+        public const int main = 0x456;
+    }
+
+    public class Strings {
+        public const int first_string = 0xabc;
+        public const int second_string = 0xbcd;
+    }
+}
+
+You would then use Resource.Drawable.icon to reference the drawable/icon.png file, or 
+Resource.Layout.main to reference the layout/main.xml file, or Resource.Strings.first_string 
+to reference the first string in the dictionary file values/strings.xml.

Raylib-cs.Android.Sample/Resources/layout/activity_main.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent">
+    <TextView 
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_centerInParent="true"
+        android:text="@string/app_text"
+    />
+</RelativeLayout>

Raylib-cs.Android.Sample/Resources/mipmap-anydpi-v26/appicon.xml

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+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+  <background android:drawable="@mipmap/appicon_background" />
+  <foreground android:drawable="@mipmap/appicon_foreground" />
+</adaptive-icon>

Raylib-cs.Android.Sample/Resources/mipmap-anydpi-v26/appicon_round.xml

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+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+  <background android:drawable="@mipmap/appicon_background" />
+  <foreground android:drawable="@mipmap/appicon_foreground" />
+</adaptive-icon>

Raylib-cs.Android.Sample/Resources/values/ic_launcher_background.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#2C3E50</color>
+</resources>

Raylib-cs.Android.Sample/Resources/values/strings.xml

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+<resources>
+    <string name="app_name">Raylib_cs.Android</string>
+    <string name="app_text">Hello, Android!</string>
+</resources>