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.ValueProviders.cs

@@ -0,0 +1,88 @@
+namespace Spectre.Console.Tests.Unit.Cli;
+
+public sealed partial class CommandAppTests
+{
+    public sealed class ValueProviders
+    {
+        public sealed class ValueProviderSettings : CommandSettings
+        {
+            [CommandOption("-f|--foo <VALUE>")]
+            [IntegerValueProvider(32)]
+            [TypeConverter(typeof(HexConverter))]
+            public string Foo { get; set; }
+        }
+
+        public sealed class IntegerValueProvider : ParameterValueProviderAttribute
+        {
+            private readonly int _value;
+
+            public IntegerValueProvider(int value)
+            {
+                _value = value;
+            }
+
+            public override bool TryGetValue(CommandParameterContext context, out object result)
+            {
+                if (context.Value == null)
+                {
+                    result = _value;
+                    return true;
+                }
+
+                result = null;
+                return false;
+            }
+        }
+
+        public sealed class HexConverter : TypeConverter
+        {
+            public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+            {
+                if (value is int integer)
+                {
+                    return integer.ToString("X");
+                }
+
+                return value is string stringValue && int.TryParse(stringValue, out var intValue)
+                    ? intValue.ToString("X")
+                    : base.ConvertFrom(context, culture, value);
+            }
+        }
+
+        [Fact]
+        public void Should_Use_Provided_Value_If_No_Value_Was_Specified()
+        {
+            // Given
+            var app = new CommandAppTester();
+            app.SetDefaultCommand<GenericCommand<ValueProviderSettings>>();
+            app.Configure(config => config.PropagateExceptions());
+
+            // When
+            var result = app.Run();
+
+            // Then
+            result.Settings.ShouldBeOfType<ValueProviderSettings>().And(settings =>
+            {
+                settings.Foo.ShouldBe("20"); // 32 is 0x20
+                });
+        }
+
+        [Fact]
+        public void Should_Not_Override_Value_If_Value_Was_Specified()
+        {
+            // Given
+            var app = new CommandAppTester();
+            app.SetDefaultCommand<GenericCommand<ValueProviderSettings>>();
+            app.Configure(config => config.PropagateExceptions());
+
+            // When
+            var result = app.Run("--foo", "12");
+
+            // Then
+            result.Settings.ShouldBeOfType<ValueProviderSettings>().And(settings =>
+            {
+                settings.Foo.ShouldBe("C"); // 12 is 0xC
+                });
+        }
+    }
+}