Rust-04 Ownership

Description	Sample Code
mutable reference	&mut varible_name
reference	&varible_name

Rust中会对变量增加一个所有权的概念，即，变量被声明时，所分配的内存（包括栈（stack）上分配和堆（heap）上分配的变量）归当前变量所有。一旦变量超出其作用域后便会将分配的内存释放掉。

let a = 5;
let b = a; // a shoule be moved, but it implemented the Copy triat


let s1 = String::from("hello");
let s2 = s1; // s1 will be moved