More refactoring

Upstream patch for setting handler priority on arch v6-m.

Use dsb instead of isb barrier on pend.

Fix issue with scheduler locking on ARM v7m.

testbench fixes

Move queue implementation to separate file. Make timers more generic.

Add ISR event queue for semaphore release events.

Make Try methods ISR safe for message queues.
Improve comments.

Merge branch 'master' of https://github.com/mneedes/mos

Add random number generator support and random pulse generator (for t…

…esting purposes).

Implement message timers