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/Data/Commands/VersionCommand.cs

@@ -0,0 +1,18 @@
+namespace Spectre.Console.Tests.Data;
+
+public sealed class VersionCommand : Command<VersionSettings>
+{
+    private readonly IAnsiConsole _console;
+
+    public VersionCommand(IAnsiConsole console)
+    {
+        _console = console;
+    }
+
+    public override int Execute(CommandContext context, VersionSettings settings)
+    {
+        _console.WriteLine($"VersionCommand ran, Version: {settings.Version ?? string.Empty}");
+
+        return 0;
+    }
+}