Add a high-resolution real-time clock #17

This PR updates our custom Clock functionality to use a high-resolution real-time clock that can be seeded from the RTC or over the network using NTP. This clock can then be converted to and from the kernel clock and used to schedule events.

I've done my best to make the code readable but it's a bit too mathematical to be easily understood. The comments should explain what each function does clearly and main.cpp should show an example of using it.

Yeah way too much math involved for my brain here, like you thought. But the comments are good enough that I understand what the code does. I think this is not bad at all then and should be merged.

Add a high-resolution real-time clock