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/Annotations/CommandArgumentAttributeTests.cs

@@ -0,0 +1,59 @@
+namespace Spectre.Console.Tests.Unit.Cli.Annotations;
+
+public sealed partial class CommandArgumentAttributeTests
+{
+    [Fact]
+    public void Should_Not_Contain_Options()
+    {
+        // Given, When
+        var result = Record.Exception(() => new CommandArgumentAttribute(0, "--foo <BAR>"));
+
+        // Then
+        result.ShouldNotBe(null);
+        result.ShouldBeOfType<CommandTemplateException>().And(exception =>
+            exception.Message.ShouldBe("Arguments can not contain options."));
+    }
+
+    [Theory]
+    [InlineData("<FOO> <BAR>")]
+    [InlineData("[FOO] [BAR]")]
+    [InlineData("[FOO] <BAR>")]
+    [InlineData("<FOO> [BAR]")]
+    public void Should_Not_Contain_Multiple_Value_Names(string template)
+    {
+        // Given, When
+        var result = Record.Exception(() => new CommandArgumentAttribute(0, template));
+
+        // Then
+        result.ShouldNotBe(null);
+        result.ShouldBeOfType<CommandTemplateException>().And(exception =>
+            exception.Message.ShouldBe("Multiple values are not supported."));
+    }
+
+    [Theory]
+    [InlineData("<>")]
+    [InlineData("[]")]
+    public void Should_Not_Contain_Empty_Value_Name(string template)
+    {
+        // Given, When
+        var result = Record.Exception(() => new CommandArgumentAttribute(0, template));
+
+        // Then
+        result.ShouldNotBe(null);
+        result.ShouldBeOfType<CommandTemplateException>().And(exception =>
+            exception.Message.ShouldBe("Values without name are not allowed."));
+    }
+
+    [Theory]
+    [InlineData("<FOO>", true)]
+    [InlineData("[FOO]", false)]
+    public void Should_Parse_Valid_Options(string template, bool required)
+    {
+        // Given, When
+        var result = new CommandArgumentAttribute(0, template);
+
+        // Then
+        result.ValueName.ShouldBe("FOO");
+        result.IsRequired.ShouldBe(required);
+    }
+}