Export functions instead of static methods

The library is quite big and it cannot be tree shaken because all of the operators are static methods.
It would be nice to have them exported from module, so unused operators could be removed from final bundle, after all we all want faster web.
Chances are you won't be using many operators like bitwise operations.
In my case, I would like to use BigInt for operations on money and I really need only basic operations.

Start by mapping the current static-method operators and the module's entry point. Define an export shape that lets unused operators be removed from the final bundle while preserving the basic operations needed for BigInt-based money use.

Written by the indexing model from the issue text.