Fix CDC configuration problem on Windows when we have a composite
device (multiple different Device Classes). Add "Interface Association
Descriptor" to make it work.
- Use CTS signals to let the FPGA and CH552 signal each other that
it is OK send UART data.
- Update the CH552 rx and frame handling logic.
- Fix minor spelling errors and indentation
- Add USB HID support.
- Introduce a small protocol to distinguish between CDC and HID data
sent over the UART.
- Add some debug printing.
- Cleanup of code and formatting.
