Closing because discussion in #303 is heading towards a different solution.

There are a few asm! instructions in support.rs, irq.rs, lock.rs and sched.rs. Also some NOPs in examples and drivers that need to be replaces with calls to Zinc intrinsics.

I'm not sure of the best way to handle the instrinsics. Maybe define a trait for them, and use a feature #cfg to import the right impl?

• nop
• bkpt
• change stack, manipulate stack pointer
• enable/disable irqs
• provide a lock primitive
• wfi instruction