Miscellaneous USB notes and naming clean-up.

firmware/usb_performance/usb.h

@@ -28,6 +28,8 @@
 
 #include "usb_type.h"
 
+// TODO: This is a lame move, requiring an extern to be defined to complete
+// the interface between this API and the application.
 extern bool usb_set_configuration(
 	usb_device_t* const device,
 	const uint_fast8_t configuration_number

firmware/usb_performance/usb_request.h

@@ -38,7 +38,7 @@ typedef enum {
 } usb_transfer_stage_t;
 
 typedef void (*usb_request_handler_fn)(
-	usb_endpoint_t* const response,
+	usb_endpoint_t* const endpoint,
 	const usb_transfer_stage_t stage
 );