Implementation for lint check

[thomasyonug]

I noticed that builtin lint check macro is still missing. An example for lint check.

#[allow(dead_code)]
fn foo() {}

There are features in lint check:

• allow, deny, forbid, warn
• lint group
• tool lint

It'll be easier to implement this if I get some suggestions from you guys.

[CohenArthur]

This is a great! It's interesting that they're not part of the list of builtin macros. They are implemented in the rustc_lint_defs crate in rustc. I think there might be a reason as to why they're not regular builtins but I haven't looked into it yet. Maybe we can implement them as regular builtins?