How do I use this project without Composer?

[hiphigi]

This may be a stupid question, but how do you install it without composer? Which files do I need to include to have the namespaces and class available to me?

[GrahamCampbell]

Just google for how to autoload any PSR-4 project. The beauty of PSR-4 is write one autoloader, and it'll work anywhere.

[Arcesilas]

Since it's possible, we can also read on the main page of the League's website:

We distribute code via Packagist and Composer.

[colinodell]

I second @GrahamCampbell's advice. While it's technically possible to download the ZIP and use it without an autoloader, it's going to be a major hassle, so I'd strongly advise against it.