Exercise Proposal: HTTP Query string builder

I've recently taken on the challenge of creating a query string builder, and I found it to be a rewarding exercise.

This is an exercise that I enjoy doing whenever I learn a new language and would like to share it.
##### Exercise:

```
Write a program that provided a list of tuples can return a HTTP query string.

For example: (Rust-specific)

Input:
let params = vec![("key1", "value1"), ("key2", "value2")];

Output:
"?key1=value1&key2=value2"
```