## string_permutation

### Instructions

Define the function `is_permutation` that returns true if the string `s1` is a permutation of `s2`, otherwise it returns false `s1` is a permutation of `s2` if all the elements in `s1` appear the same number of times in `s2` and all the characters in `s1` appear in `s2` even if in different order)

### Expected Function

```rust
fn is_permutation(s1: &str, s2: &str) -> bool {
}
```

### Usage

Here is a program to test your function.

```rust
fn main() {
	let word = "thought";
	let word1 = "thougth";
	println!(
		"Is `{}` a permutation of `{}`? = {}",
		word,
		word1,
		is_permutation(word, word1)
	);
}
```

And its output

```console
student@ubuntu:~/[[ROOT]]/test$ cargo run
Is `thought` a permutation of `thougth`? = true
student@ubuntu:~/[[ROOT]]/test$
```