Make build work (#546)

The mbedtls example has caused problem in the main build a number of
times. By making it a standalone `cargo new --bin`, we can keep it in
the source tree as a good example but avoid having it break the main
build.

Also, fix some clippy lints.

examples/mbedtls/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "mbedtls-example"
+version = "0.0.1"
+edition = "2021"
+
+
+[dependencies]
+mbedtls = { version = "0.8.1" }

examples/mbedtls/README.md

@@ -0,0 +1,9 @@
+mbedtls-example
+===============
+
+To run this example you need to `cd` into the directory and use `cargo run`.
+
+```
+cd ureq/exampled/mbedtls
+cargo run
+```

examples/smoke-test/main.rs

@@ -5,7 +5,6 @@ use std::time::Duration;
 use std::{env, error, fmt, result};
 
 use log::{error, info};
-use ureq;
 
 #[derive(Debug)]
 struct Oops(String);
@@ -77,7 +76,7 @@ fn get_many(urls: Vec<String>, simultaneous_fetches: usize) -> Result<()> {
 }
 
 fn main() -> Result<()> {
-    let args = env::args();
+    let mut args = env::args();
     if args.len() == 1 {
         println!(
             r##"Usage: {:#?} top-1m.csv
@@ -94,11 +93,11 @@ using 50 threads concurrently.
         return Ok(());
     }
     env_logger::init();
-    let file = std::fs::File::open(args.skip(1).next().unwrap())?;
+    let file = std::fs::File::open(args.nth(1).unwrap())?;
     let bufreader = BufReader::new(file);
     let mut urls = vec![];
     for line in bufreader.lines() {
-        let domain = line?.rsplit(",").next().unwrap().to_string();
+        let domain = line?.rsplit(',').next().unwrap().to_string();
         urls.push(format!("http://{}/", domain));
         urls.push(format!("https://{}/", domain));
         urls.push(format!("http://www.{}/", domain));