Add rules for merging to master

[notdanilo]

• CI must be passing
• The PR must have been reviewed and approved by at least one reviewer
• No warning messages in the build process

Merging should be blocked otherwise.

[notdanilo]

These deny slows down development a bit. Sometimes I just want to remove something to test and I have to remove unused uses. I think it makes sense to deny(unstable_features), but it's OK to keep the other. Everyone should remember to cleanup the warning before pushing. We can even make the CI to fail if it sees warning messages.

#![deny(unstable_features)]
// #![deny(
//     unused_must_use,
//     unused_mut,
//     unused_imports,
//     unused_import_braces
// )]