Deleted StdDescriptors.c, renamed USB_GetDescriptor() to CALLBACK_USB_GetDescriptor, moved ConfigDescriptor.c/.h from the LUFA/Drivers/USB/Class/ directory to LUFA/Drivers/USB/HighLevel/ in preperation for the new USB class APIs.

All comments in the library, bootloaders, demos and projects have now been spell-checked and spelling mistakes/typos corrected.

Altered DFU bootloader to use the signature byte constants located in the avr-libc part headers, rather than redefining them in Descriptors.h.