Featureless entrypoints

[aumetra]

Closes #1627

After merging and releasing this, we can just remove any and all mention of the library feature :P

[chipshort]

Nice stuff!
Can we test this using one of the actual contracts? Like one of them importing another one and then showing that it compiles and that it still works correctly in an integration test?

[aumetra]

Yep, that's the idea. Gonna add that tomorrow and then we can hit the big merge button

[webmaster128]

Very nice. It feels a bit too easy to be true to be honest. But I don't see any issue with that approach.

[aumetra]

It feels a bit too easy to be true to be honest

Kinda does, doesn't it. But the CI checks seem to verify that it does work (also did some tests with proc-macros first; but it seems that it does what it should do)

[chipshort]

Looks very nice!
Can you do some cleanup on the new contracts? I would remove the license files, .editorconfig, .gitignore and the README of the inner-contract.