Add more Rust-like macros

[udoprog]

This introduces FormatArgs as a utility type to parse and expand format arguments.

It is now used in panic!, assert_eq!, and assert! to allow for formatting a message there, like with the Rust macros:

let food = "Tofu";
panic!("I sure do like {food}", food = food);

I've also suppressed the warning about using a template without expansions. This is accomplished by adding a parameter to builtin, like #[builtin(literal)] which signals that the template was caused by a literal and appropriately should generate warnings. The warning is not emitted otherwise.