Rename the template_for header.

C++26 (I hope) is supposed to have this syntax:

```
template for( const auto &element: aggregate )
{
	...;
}
```

Thus, I've adjusted this gadget to have a similar name, to enable
simple mechanical code changes.  From Alepha, you'd use it
thus:

```
template_for( aggregate ) <=[&]( const auto &element )
{
	...;
};
```

template_for.test/0.cc

@@ -0,0 +1,42 @@
+static_assert( __cplusplus > 2023'00 );
+
+#include "../template_for.h"
+
+#include <Alepha/Testing/test.h>
+#include <Alepha/Testing/TableTest.h>
+
+#include <sstream>
+
+#include <Alepha/Utility/enroll.h>
+
+static auto init= Alepha::Utility::enroll <=[]
+{
+	using namespace Alepha::Testing::literals;
+	using namespace Alepha::Testing::exports;
+
+	struct Example
+	{
+		int x;
+		std::string s;
+		int y;
+	};
+
+	"Can one `template_for` each over a simple struct and get the members into a string?"_test <=TableTest
+	<
+		[]( Example ex )
+		{
+			using Alepha::template_for;
+			std::ostringstream oss;
+			template_for( ex ) <=[&]( const auto &element )
+			{
+				oss << element << std::endl;
+			};
+
+			return oss.str();
+		}
+	>
+	::Cases
+	{
+		{ "Simple case", { { 42, "Hello World", 1138 } }, "42\nHello World\n1138\n" },
+	};
+};

template_for.test/CMakeLists.txt

@@ -0,0 +1 @@
+unit_test( 0 )