Rename "maybe" things to "option" in core::option

[catamorphism]

This is my fault -- there are functions called from_maybe, maybe, and so on. Since we spell "maybe" as "option" in Rust, these should be renamed.

[brson]

I find the distinction between these two functions impossible to remember. I know they are taken directly from haskell, but it would be awesome if we could come up with more descriptive names, maybe that follow conventions we've established in the str and vec modules.

I had an issue open to do such for a while but blanked on any better names so closed it.

[brson]

And may as well. They all just read to me as 'this is a function that might do something' - great.