Timestamps - Wall clock vs. monotonic requirements

[davidlenfesty]

Migration of conversation about/tracking of library requirements for timestamping from #75.

Brief summary:

• Current implementation only provides infrastructure for monotonic clocks, without any regard for wall clock support.
• We want to have some form of infrastructure in place for handling wall clock.

I have no opinions on how to do this at the moment, I will need to do some thinking/research on requirements and come back here, but I do believe that this is a blocking issue for v1. Even if wall clock support isn't included in the initial release there has to be a plan in place.