Default implementation using macros
Use Default2 to set default value of each field using a macro:
```rust use default2::Default2;
struct Process { #[default(10)] id: i32, #[default("main".into())] name: String, #[default(num_cpus::get())] cpus: usize, payload: u64, } ```
The following code will be generated:
```rust struct Process { id: i32, name: String, cpus: usize, payload: u64, }
impl Default for Process { fn default() -> Self { Self { id: 10, name: "main".into(), cpus: num_cpus::get(), payload: Default::default(), } } } ```