Support #[allow] etc logic on a per macro level

Support #[allow] etc logic on a per macro level

This commit extends the current unused macro linter
to support directives like #[allow(unused_macros)]
or #[deny(unused_macros)] directly next to the macro
definition, or in one of the modules the macro is
inside. Before, we only supported such directives
at a per crate level, due to the crate's NodeId
being passed to session.add_lint.

We also had to implement handling of the macro's
NodeId in the lint visitor.