Add High-Resolution Timer

[ammrat13]

The timer is at REG_HIGHRESTIME_ADDR, and it's the number of milliseconds that have elapsed since the current second started.

Closes #29

[sameer-s]

LGTM, just a few questions/comments:

• std::chrono::system_clock makes no guarantees about precision. However this should be ok in this case due to real-world behavior:
• What exactly is the use-case? Is there a way we can get both the standard and high-res clocks in sync to get the "precise current time"?

[ammrat13]

LGTM, just a few questions/comments:

• std::chrono::system_clock makes no guarantees about precision. However this should be ok in this case due to real-world behavior:
• What exactly is the use-case? Is there a way we can get both the standard and high-res clocks in sync to get the "precise current time"?

I believe this can be dealt with by reading the milliseconds, then seconds, then milliseconds, then seconds. It's jank, but it should work. Still, it might be worth prettying up the interface to avoid this problem.

[ammrat13]

A possible alternative interface is as follows. Have a timer status register along with the seconds and milliseconds register. The data registers are updated when anything is written to the status register.

[sameer-s]

Gotcha, well this should work for now as you described. Merging it in, but we might add a new interface later.