A simple trait to mark up the struct and help recognize the struct's attributes.
```rust use acts_tag::{Tags, Value}; use std::any::Any;
pub struct MyTags {
#[tag]
pub tag1: String,
#[tag]
pub tag2: i32,
pub others: String,
}
fn main() {
let t = MyTags {
tag1: "a".tostring(),
tag2: 5,
others: "others".tostring(),
};
asserteq!(t.tagkeys(), vec![ "tag1", "tag2" ]);
for tagkey in t.tagkeys() {
let value = t.tagvalue(tagkey).unwrap();
println!("value {} = {:?}", tagkey, value);
}
let value = t.tagvalue("tag1").unwrap();
asserteq!(value.to::