Add compatibility with FNA (#106)

* Rectangles in FNA don't support initialization with two vectors. TextureAtlas.cs changed to use the Rectangle constructor with four parameters.

* added MonoGame.Aseprite.FNA.csproj, which presumably would be the least surprising way of adding Monogame.Aseprite to a FNA project

* removed from FNA project file item groups and property groups related to NuGet package stuff

source/MonoGame.Aseprite/MonoGame.Aseprite.FNA.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <!-- Project level compilation properties -->
+    <PropertyGroup>
+        <TargetFrameworks>net8.0</TargetFrameworks>
+        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    </PropertyGroup>
+
+    <!-- Project References -->
+    <ItemGroup>
+      <ProjectReference Include="..\..\..\AsepriteDotNet\source\AsepriteDotNet\AsepriteDotNet.csproj" />
+      <ProjectReference Include="..\..\..\FNA\FNA.Core.csproj" />
+    </ItemGroup>
+
+</Project>

source/MonoGame.Aseprite/TextureAtlas.cs

@@ -128,7 +128,7 @@ public TextureRegion CreateRegion(string name, int x, int y, int width, int heig
     /// </exception>
     /// <returns>The <see cref="TextureRegion"/> created by this method.</returns>
     public TextureRegion CreateRegion(string name, Point location, Point size) =>
-        CreateRegion(name, new Rectangle(location, size));
+        CreateRegion(name, new Rectangle(location.X, location.Y, size.X, size.Y));
 
     /// <summary>
     /// Creates a new <see cref="TextureRegion"/> and adds it to this <see cref="TextureAtlas"/>.