Allow real Timer suspend/resume and set timer value

[jfpoilpret]

[Issue was oroginally reported by email from Slawomir Dors]
The current suspend() API does not really suspend a Timer but only suspends attached interruptions.
It would be nice to really suspend a Timer (having its counter frozen) and later resume it.
In addition, it can be useful to set the counter value sometimes.

[jfpoilpret]

API change proposal:

1. change reset()/reset_() to reset(TYPE)/reset_(TYPE)
2. add suspend_timer() API that stops the timer (but does not change any current settings)
3. add resume_timer() API that runs timer again (and reuses previous settings)

[jfpoilpret]

In addition, we should probably rename current suspend()/resume() API to suspend_interrupts()/resume_interrupts() to make it clearer what they do (also update API doc).

[jfpoilpret]

Implemented on master branch.