USB device support

Samples that demonstrate USB device support.

• Console over USB CDC ACMOutput "Hello World!" to the console over USB CDC ACM.
• USB Audio asynchronous explicit feedback sampleUSB Audio 2 explicit feedback sample playing audio on I2S.
• USB Audio asynchronous implicit feedback sampleUSB Audio 2 implicit feedback sample playing stereo and recording mono audio on I2S interface.
• USB Audio headsetImplement a USB Audio headset device with audio IN/OUT loopback.
• USB Audio microphone & headphonesImplement a USB Audio microphone + headphones device with audio IN/OUT loopback.
• USB CDC-ACMUse USB CDC-ACM driver to implement a serial port echo.
• USB DFU (Device Firmware Upgrade)Implement device firmware upgrade using the USB DFU class driver.
• USB HID keyboardImplement a basic HID keyboard device.
• USB HID mouseImplement a basic HID mouse device.
• USB Mass StorageExpose board's RAM or FLASH as a USB disk using USB Mass Storage driver.
• USB shellUse shell commands to interact with USB device stack.
• USB testing applicationTest USB device drivers using a loopback function.
• WebUSBReceive and echo data from a web page using WebUSB API.