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/Extensions/Spectre.Console.Json/Syntax/JsonString.cs

@@ -0,0 +1,26 @@
+namespace Spectre.Console.Json.Syntax;
+
+/// <summary>
+/// Represents a string literal in the JSON abstract syntax tree.
+/// </summary>
+public sealed class JsonString : JsonSyntax
+{
+    /// <summary>
+    /// Gets the lexeme.
+    /// </summary>
+    public string Lexeme { get; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="JsonString"/> class.
+    /// </summary>
+    /// <param name="lexeme">The lexeme.</param>
+    public JsonString(string lexeme)
+    {
+        Lexeme = lexeme;
+    }
+
+    internal override void Accept<T>(JsonSyntaxVisitor<T> visitor, T context)
+    {
+        visitor.VisitString(this, context);
+    }
+}