Add template with code in a Main method (#647)

This will allow for examples which are just statements.
(Also adds example in 16.1 Arrays to show how to use it.)

Towards #646

Author: jskeet

standard/arrays.md

@@ -10,6 +10,7 @@ The element type of an array can itself be an array type ([§16.2.1](arrays.md#1
 
 > *Example*:
 >
+> <!-- Example: {template:"code-in-main", name:"PascalArrayDeclarations"} -->
 > ```csharp
 > int[][] pascals = 
 > {

tools/example-templates/code-in-main/Program.cs

@@ -0,0 +1,7 @@
+class Program
+{
+    static void Main()
+    {
+        $example-code
+    }
+}

tools/example-templates/code-in-main/Project.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>disable</Nullable>
+    <AssemblyName>$example-name</AssemblyName>
+  </PropertyGroup>
+
+</Project>