Add proc macro crate for several proc macros we want

[Amjad50]

Currently we have cmdline_struct and alsotesting::test macros which surround struct/functions.

There are downsides to this:

• adds more indentation
• the formatter doesn't recognize the inner part as the struct/function anymore so it struggle with formatting it.

There is this very nice crate: https://crates.io/crates/macro_rules_attribute. And it works really well.

But I don't want to add more deps for such a simple thing that can be done in proc macro, so a good exercise