Recording works!

I implemented an I2S Receiver and wired it up to USB.
After fixing a couple of showstopper bugs, audio input it is now working.
You can now record from the DECA board via its line input.

Bugfixes

• left and right channels now don't trade places anymore every couple of seconds due to a bugfix in the I2S core in nmigen-library

Audio output works!

First working release, where the audio output works.
Audio input is still not possible due to missing I2S receiver core.