Update bc_usb_cdc header

bcl/inc/bc_usb_cdc.h

@@ -3,9 +3,29 @@
 
 #include <bc_common.h>
 
+//! @addtogroup bc_usb_cdc bc_usb_cdc
+//! @brief USB CDC communication library
+//! @{
+
+//! @brief Initialize USB CDC library
+
 void bc_usb_cdc_init(void);
-void bc_usb_cdc_start(void);
+
+//! @brief Write buffer to USB CDC (non-blocking call)
+//! @param[in] buffer Pointer to buffer to be written
+//! @param[in] length Number of bytes to be written
+//! @return true On success
+//! @return false On failure
+
 bool bc_usb_cdc_write(const void *buffer, size_t length);
+
+//! @brief Read buffer from USB CDC (non-blocking call)
+//! @param[out] buffer Pointer to buffer to be read
+//! @param[in] length Number of bytes to be read
+//! @return Number of bytes read
+
 size_t bc_usb_cdc_read(void *buffer, size_t length);
 
+//! @}
+
 #endif // _BC_USB_CDC_H