Fix redefinition warning when USB_DEVICE_ONLY is set on an AVR which does not support USB host mode.

Changed per-device controller preprocessor checks over to per-device series for better device control.

Fixed error in Endpoint.c using HSOFI rather than SOFI for counting elapsed milliseconds.

Move StdRequestType.h, StreamCallbacks.h, USBMode.h from the LowLevel USB driver directory to the HighLevel USB driver directory, where they are more suited.

Fixed documentation typoes and preprocessor checks relating to misspellings of the USE_RAM_DESCRIPTORS token (thanks to Ian Gregg).