更新版本号至0.3.1，准备发布包含面向对象编程支持的重大更新。

Author: HelloAIXIAOJI

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "CodeNothing"
-version = "0.2.7"
+version = "0.3.1"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html