add chapter 12 solutions

implementation/12/src/Exception/InternalServerError.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Exception;
+
+use Exception;
+
+final class InternalServerError extends Exception
+{
+}

implementation/12/src/Exception/MethodNotAllowed.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Exception;
+
+use Exception;
+
+final class MethodNotAllowed extends Exception
+{
+}

implementation/12/src/Exception/NotFound.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace Lubian\NoFramework\Exception;
+
+use Exception;
+
+final class NotFound extends Exception
+{
+}