Create a macro rule called `hash_map` to initialize and declare an`HashMap` at the same time, very similar to what `vec!` macro does for `Vector`.
Create a macro rule called `hash_map` to initialize and declare a `HashMap` at the same time, very similar to what `vec!` macro does for `Vector`.
> Your macro should accept both leading commas and non leading commas syntax to be more flexible in terms of coding style and reflect the language general style.
> Your macro should accept both leading and non leading commas syntax to be more flexible in terms of coding style and reflect the language general style.