small layout change to move backspace, remove delete, and add tab on layer1
adding usb_extra.c/.h from Hasu's tmk code. Won't compile as is.
usb_extra.c now compiles
adding media keys

taken from Hasu codebase (https://github.com/tmk/tmk_keyboard) usb.c/.h
and usb_extra.c/.h, though these files only have the PJRC
copyright/license in the header