Remove use of avr-libc specific ATOMIC_BLOCK, replace with a new per-architecture set of inline functions to retrieve and manipulate the global interrupt enable bit for each architecture.
Add in documentation for the USB controller common interrupt routine which must be linked to the interrupt controller in the user application on the AVR32 UC3 architecture.
Fixed calculation of timer register reload values derived from F_CPU; must subtract one from the division result for the compare value to be correct.
Change AVRISP-MKII rescue clock speed to 4MHz to ensure that a 125KHz ISP speed works regardless of the target's fuses (i.e. DIV8 set).