[META] Performance

[oliverklee]

• memoize/cache the results of the ApplicationStructure methods
• superfast requests: TurboLinks
• document that XHProf is recommended for profiling
• use a faster YAML reader https://github.com/koenpunt/yaml-php-benchmark
• cache the entity manager and the Doctrine registry in the Bootstrap class
• investigate which services to make lazy (maybe the repositories?) https://symfony.com/doc/current/service_container/lazy_services.html
• when using native PHP functions, always call them with a leading backslash: https://github.com/Roave/FunctionFQNReplacer