Preparations for the 1.0 release

* Less cluttered solution layout.
* Move examples to a repository of its own.
* Move Roslyn analyzer to a repository of its own.
* Enable central package management.
* Clean up csproj files.
* Add README file to NuGet packages.

src/Tests/Spectre.Console.Cli.Tests/Unit/CommandAppTests.Async.cs

@@ -0,0 +1,70 @@
+namespace Spectre.Console.Tests.Unit.Cli;
+
+public sealed partial class CommandAppTests
+{
+    public sealed class Async
+    {
+        [Fact]
+        public async Task Should_Execute_Command_Asynchronously()
+        {
+            // Given
+            var app = new CommandAppTester();
+            app.SetDefaultCommand<AsynchronousCommand>();
+            app.Configure(config =>
+            {
+                config.PropagateExceptions();
+            });
+
+            // When
+            var result = await app.RunAsync();
+
+            // Then
+            result.ExitCode.ShouldBe(0);
+            result.Output.ShouldBe("Finished executing asynchronously");
+        }
+
+        [Fact]
+        public async Task Should_Handle_Exception_Asynchronously()
+        {
+            // Given
+            var app = new CommandAppTester();
+            app.SetDefaultCommand<AsynchronousCommand>();
+
+            // When
+            var result = await app.RunAsync(new[]
+                        {
+                        "--ThrowException",
+                        "true",
+                        });
+
+            // Then
+            result.ExitCode.ShouldBe(-1);
+        }
+
+        [Fact]
+        public async Task Should_Throw_Exception_Asynchronously()
+        {
+            // Given
+            var app = new CommandAppTester();
+            app.SetDefaultCommand<AsynchronousCommand>();
+            app.Configure(config =>
+            {
+                config.PropagateExceptions();
+            });
+
+            // When
+            var result = await Record.ExceptionAsync(async () =>
+                    await app.RunAsync(new[]
+                        {
+                        "--ThrowException",
+                        "true",
+                        }));
+
+            // Then
+            result.ShouldBeOfType<Exception>().And(ex =>
+            {
+                ex.Message.ShouldBe("Throwing exception asynchronously");
+            });
+        }
+    }
+}