USB1 ↔ USB2 bidirectional audio works

Now USB2 ↔ USB1 audio sending/receiving works both ways

Now includes a new ADAT transceiver implementation which
uses a fraction of its resources.

Also included in this release is a USB analyzer trace of USB1 which
is a square LFO going from zero to full. This demonstrates the low latency
of the device of about 0.2ms.

Bitstream files are for the EP4CE55, which I use for development convenience.