Macro hashmap 

macro_rules! hashmap {
    ($capacity:expr, { $($key:expr => $value:expr),* }) => { ... };
    (capacity = $capacity:expr, { $($key:expr => $value:expr),* }) => { ... };
    { $($key:expr => $value:expr),* } => { ... };
}

快速构建一个std::collections::HashMap

use utils_soeur::hashmap;

hashmap! {
    1 => 'a'
};

with_capacity:

use utils_soeur::hashmap;

hashmap! (2, {
    1 => 'a',
    2 => 'b'
});