Return Self from Usbd::new

[jonas-schievink]

This makes the device_address method usable, and allows adding more methods in the future (although they'll only work before the bus is initialized).

Also build/check the example by default.

cc #8

[jonas-schievink]

Looking closer, it looks like you're meant to access the UsbBus implementor (immutably) by calling UsbDevice::bus.

I still think returning Self here makes more sense, as it is much more in line with good API design practices, and we can then add &mut self methods to enforce their use before the USB bus is actually made active.

Hence,
bors r+

[bors]

Build succeeded:

• ci