figure out what should be in stdlib vs a separate module

[vito]

[vito]

I think it's actually OK for .strings to be a separate module, but I'm just gonna look around for other things that seem out of place or could be moved/consolidated.

• List functions can exist in Ground because lists are core to the language semantics; at least some of them need to be just for bootstrapping.
• [ ] If an intuitive boundary can be found, "advanced" list functions could be put in a separate module, but this should be done with caution (could be more confusing than it's worth - maybe an extensive Ground is a good thing?)
• Strings aren't core to semantics or needed for bootstrapping, and there's probably lots of overlap with list functions, so they should be in a module (as they are now).
• [x] .durations should just be .time
• [x] (time) -> (time:measure)
• [ ] (look for more)

[vito]

Moving this all the way to 1.0 when it really matters.