Rename file.
Make EP0 64 byte big.

The USB Device library just assumes we use a 64 byte big EP0.
Fix long line in usb_callbacks.c
Remove unused code.

There are definitions in the library configuration header that aren’t
even used by the library.
Refactor device descriptor code.

Provide an error string for strings that should not even be queried.
Fix configuration descriptor.

The authors of the usb library apperently think it’s a good idea to
overwrite defacto constant data (the configuration descriptor).
Fix usb descriptors.

The device does now enumerate succesfully.
Make string descriptors const.