re-add "exports"

[ljharb]

See #133 for background.

Before doing this, ensure tests are added that require, and import, with and without extensions, any arbitrary AO, from outside the package, that verify:

• the AO is successfully brought in
• only expected warnings are generated

This may require changes in node 12, 14, and 16 to be viable.

[mhmdbkry]

https://github.com/nvm-sh/nvm