refactor built-in resolvers

[omry]

Reorganizing built-in resolvers.

I am also thinking about an alternative layout with a single file per module:

oc/__init__.py # oc module
oc/dict.py    # oc.dict module 

[odelalleau]

Sounds good! (not sure we care about defining __all__ but why not)

[omry]

if you just import in init and not use it's triggering a lint warning

Oh I see -- I didn't realize that.

the alternative layout should probably eliminate the need for it

New layout works for me too.

[Jasha10]

Looks good to me.

[omry]

Switched to new layout, I think it's significantly cleaner.