Provide a way to export a Paket-based project as a .unitypackage

[kibiz0r]

If we have #13, then a natural next step is to let Unity developers choose to share their projects as .unitypackages, which are suitable for import through the editor or uploading to the asset store.

[Larusso]

If you're not against using gradle:
https://github.com/wooga/atlas-unity -> gradle unity wrapper
https://github.com/wooga/atlas-paket -> gradle paket wrapper

see also our opinionated release plugin which does exactly that https://github.com/wooga/atlas-release.