Rust Macros Designators Introduction

# Introduction

In this lab, we are introduced to the concept of designators in Rust macros. Designators are used to prefix the arguments of a macro and are type annotated. Some examples of designators include `ident` for variable/function names, `expr` for expressions, `block` for blocks of code, and `pat` for patterns. These designators are used within macro rules to generate code based on the provided arguments.

> **Note:** If the lab does not specify a file name, you can use any file name you want. For example, you can use `main.rs`, compile and run it with `rustc main.rs && ./main`.