feat: support directive on variable definition

[saihaj]

Closes #60

[tailhook]

I'm okay with changes. But

1. Please add the test
2. If you submit formatting changes, please make it a separate commit (although I'm not sure it make sense as it actively made code worse in one place I've commented below).

[tailhook]

This made code worse, and hard to compare. The original formatting is not an accident it's done to have it easier to compare.

[LegNeato]

You can use #[rustfmt::skip] here FWIW

[saihaj]

wait there is no CI that runs these tests 🤔

[tailhook]

Ah, yes, it's because travis stopped working with github at some point. Should setup a github actions instead. But this doesn't mean there are no tests or that we don't care if they are there.