expression_simplify 1.0.1

# <div align="center">Expression Simplify</div>

> You can find the crate on **https://crates.io/crates/expression_simplify**

​	The program is a Rust library crate in the use of simplifying math expression, its function is based on the HW1 of the first Unit of Object Oriented course of SCSE, BUAA.

> **如何在Rust中实现多态**
>
> * 定义一个trait
> * 为不同类型实现trait
> * 使用特征对象``Box<dyn Trait>`` 动态指针

* ``version 1.0.0``: hw1