Macro format 

macro_rules! format {
    ($($toks:tt)*) => { ... };
}

Conceptually equivalent to ArcStr::from(format!("...", args...)).

In the future, this will be implemented in such a way to avoid an additional string copy which is required by the from operation.

Example

let arcstr = arcstr::format!("testing {}", 123);
assert_eq!(arcstr, "testing 123");