0.5.8 goals and TODO list updated

[Artem Kachitchkine]

> It's about being specific - Lock() means "please don't invoke any
> methods on the device object, I'm busy using it" while InhibitPolling()
> means "please stop polling for media changes". These use-cases are
> mutually exclusive.

Right. There's one thing that makes these two methods alike: if a process exits 
without invoking the "un"-method, HAL should enforce it.

We could probably generalize this idea beyond storage: for any device class, if 
it requires device activity, userland or kernel, to keep its state up to date, a 
pair of methods (Freeze/Unfreeze?) could be used to suspend this activity 
temporarily.

-Artem.