Fix PSR-12, docblocks and add proper arguments types in ContainerInterface

[ArrMeeR]

I found a few little mistakes while browsing the framework's code :)

[jpresutti]

@ArrMeeR, the files you modified here were copied as is from the repos in https://github.com/php-fig and are deliberately untouched. While I would love for them to follow those standards and approve this PR, because of the nature of them being externally defined interfaces, I can't.

If you have any other things you wish to work on though, PLEASE by all means do.

(For anyone wondering why the interfaces were included directly, to allow ease of install for people who don't wish to use composer)