Update to be react 16 compitable

[dchhetri]

This might just be as little work as updating peer dependency

[harsimranb]

I haven't investigated the new Context API in react 16, but I wonder how much work it is to start using that.

[klimashkin]

I would recommend my https://github.com/klimashkin/css-modules-theme, it's much faster and is react version agnostic.