Standardize core/std naming conventions

[brson]

For the most-used modules, our naming conventions have been slowly coming into alignment, but we need to scrutinize everything to make sure the libs are consistent.

[brson]

It came up today that core::option has a bunch of similarly-named functions whose purposes I can never remember. Some of them probably can be renamed according to the conventions in core::vec.

[brson]

I stared at core::option for a while but couldn't think of anything better. Those functions are named for their haskell counterparts.

[brson]

I'm pretty happy with the state of core right now, except for #2019