hal::*::lock: Initial commit

This is a basic locking primitive for buillding synchronization
primitives.
hal::cortex_m3::sched: Add CritSection

This implements a simple abstraction for critical sections where
interrupts must be disabled.
lib::shared: Initial commit

This is a simple container for thread-safe state with access guarded by
a CritSection.
lib::queue: Initial commit

This implements a simple thread-safe queue.
os::task: Add support for blocking
os::mutex: Initial commit
os::cond_var: Initial commit
Merge pull request #11 from bgamari/mutex

Added a few synchronization primitives.
Detached GPIO from GPIOConf (as it should have been in the first place).
Added basic gpio interrupt handling.
Bad ugly code for IRQ handling.
Added basic mrf driver and test application. Compiles but no tx/rx code yet.
Added sending code, demo now can talk to other devices.
Added basic irq handler.
A bit cleaner code, still not really the best option. Also, huge.
Updated for libcore.