USB_VBUS is not an alternate function, it is an additionnal function which is
always enabled.
If configured as an alternate function, it will draw current from VBUS.
The unique serial number from the device unique signature block was never used
in any examples. Add it to the these two usb midi examples, to have a user for
this api available for reference.
Be specifically careful with the usb examples. There is likely some
breakage to be expected, not sure I updated all the drivers to the
correct types for the respective chips.
Tested on STM32F4Discovery with Linux host using both amidi (raw
messages to/from device) and a synthesizer (note on/off) and on
Windows 7 using MIDI-OX.
