feat(exception): Register global exception handler

This handler catches uncaught exceptions and prints their message
and stack trace.

autoload.php

@@ -12,3 +12,8 @@ spl_autoload_register(function ($className) {
         require_once $file;
     }
 });
+
+set_exception_handler(function ($exception) {
+    echo "Uncaught exception: " , $exception->getMessage(), "\n";
+    echo $exception->getTraceAsString();
+});