Minor documentation improvements.

LUFA/Common/Attributes.h

LUFA/Common/BoardTypes.h

LUFA/Common/Common.h

LUFA/Drivers/Board/Buttons.h

LUFA/Drivers/Board/Dataflash.h

LUFA/Drivers/Board/Joystick.h

LUFA/Drivers/Board/LEDs.h

LUFA/Drivers/Misc/RingBuffer.h

LUFA/Drivers/Misc/TerminalCodes.h

LUFA/Drivers/Peripheral/AVRU4U6U7/ADC.h

LUFA/Drivers/Peripheral/AVRU4U6U7/TWI.h

LUFA/Drivers/Peripheral/SPI.h

LUFA/Drivers/Peripheral/Serial.h

LUFA/Drivers/Peripheral/SerialStream.h

LUFA/Drivers/USB/Class/Common/Audio.h

LUFA/Drivers/USB/Class/Common/CDC.h

LUFA/Drivers/USB/Class/Common/HID.h

LUFA/Drivers/USB/Class/Common/MIDI.h

LUFA/Drivers/USB/Class/Common/MassStorage.h

LUFA/Drivers/USB/Class/Common/RNDIS.h