Spell check source code, fix mistakes.

Demos/Device/ClassDriver/AudioInput/AudioInput.c

Demos/Device/ClassDriver/AudioOutput/AudioOutput.c

...Device/Incomplete/TestAndMeasurement/TestAndMeasurement.c

Demos/Device/LowLevel/KeyboardMouse/KeyboardMouse.c

Demos/Host/ClassDriver/MIDIHost/MIDIHost.c

Demos/Host/LowLevel/MassStorageHost/Lib/MassStoreCommands.c

LUFA/Common/ArchitectureSpecific.h

LUFA/Common/Attributes.h

LUFA/Drivers/Board/Buttons.h

LUFA/Drivers/Board/Joystick.h

LUFA/Drivers/Board/LEDs.h

LUFA/Drivers/Peripheral/AVR8/ADC_AVR8.h

LUFA/Drivers/USB/Class/Device/AudioClassDevice.h

LUFA/Drivers/USB/Class/Device/MIDIClassDevice.h

LUFA/Drivers/USB/Class/Host/AndroidAccessoryClassHost.h

LUFA/Drivers/USB/Class/Host/HIDClassHost.h

LUFA/Drivers/USB/Class/Host/MIDIClassHost.h

LUFA/Drivers/USB/Core/AVR8/USBController_AVR8.h

LUFA/Drivers/USB/Core/ConfigDescriptor.h

LUFA/Drivers/USB/Core/Events.h