Document canonical value presentation

[philrz]

What's Changing

This is my attempt to document how the tools present values in a canonical form in the human-readable output formats such as SUP.

Why

When fielding community inquiry #5910 and writing up a response, I recognized that this topic might benefit from a little more coverage.

Details

I expect that some aspects of canonical value presentation shown here would be unsurprising to most users, e.g., dropping trailing zeros in floating point values. OTOH, things like the duration type may be slightly less familiar to users, leading to confusion such as expressed in #5910. While docs enhancements like I'm doing here may not guarantee future users would never be confused by such things again, I figure it doesn't hurt to cover it somewhere, plus it gives me something in the docs to point at if similar questions from users come up in the future.

[philrz]

We've discussed this one and there's consensus that it probably shouldn't be merged in its current form, but @mccanne has expressed an interest in addressing the concern somehow in the ongoing revisions to the SUP format and related docs, so we're holding this one open as a reminder of that.