I added `ureq::get("http://example.com")` to a toy program and was very confused when it did nothing.
Change `Request` to give a warning if unsent:
```
warning: unused `ureq::Request` that must be used
--> src/main.rs:48:5
|
48 | ureq::get("http://example.com");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(unused_must_use)]` on by default
= note: Requests do nothing until consumed by `call()`
```
