Replace CDC interface numbers with enums.

Bootloaders/CDC/Descriptors.c

Bootloaders/HID/Descriptors.c

Bootloaders/Printer/Descriptors.h

Demos/Device/ClassDriver/DualVirtualSerial/Descriptors.c

Demos/Device/ClassDriver/Keyboard/Descriptors.h

Demos/Device/ClassDriver/Keyboard/Keyboard.c

...Device/ClassDriver/KeyboardMouseMultiReport/Descriptors.c

...river/KeyboardMouseMultiReport/KeyboardMouseMultiReport.c

Demos/Device/ClassDriver/RNDISEthernet/Descriptors.c

Demos/Device/ClassDriver/VirtualSerial/Descriptors.c

...Device/ClassDriver/VirtualSerialMassStorage/Descriptors.c

Demos/Device/ClassDriver/VirtualSerialMouse/Descriptors.c

Demos/Device/LowLevel/DualVirtualSerial/Descriptors.c

Demos/Device/LowLevel/Joystick/Descriptors.c

Demos/Device/LowLevel/Keyboard/Descriptors.c

Demos/Device/LowLevel/KeyboardMouse/Descriptors.c

Demos/Device/LowLevel/Mouse/Descriptors.c

Demos/Device/LowLevel/RNDISEthernet/Descriptors.c

Demos/Device/LowLevel/VirtualSerial/Descriptors.c

Projects/Benito/Descriptors.c