Add test.sh. (#173)

This emulates the test matrix that gets run in CI, making it easier to
find failures locally.

There was one conflict in the matrix: when JSON is enabled and TLS is
disabled, two of the doctests would fail. This was previous worked
around as an exclude in the github workflow. I changed the JSON doctest
to use HTTP instead.

src/response.rs

@@ -391,7 +391,7 @@ impl Response {
     ///
     /// ```
     /// let resp =
-    ///     ureq::get("https://ureq.s3.eu-central-1.amazonaws.com/hello_world.json")
+    ///     ureq::get("http://ureq.s3.eu-central-1.amazonaws.com/hello_world.json")
     ///         .call();
     ///
     /// let json = resp.into_json().unwrap();
@@ -436,7 +436,7 @@ impl Response {
     /// }
     ///
     /// let resp =
-    ///     ureq::get("https://ureq.s3.eu-central-1.amazonaws.com/hello_world.json")
+    ///     ureq::get("http://ureq.s3.eu-central-1.amazonaws.com/hello_world.json")
     ///         .call();
     ///
     /// let json = resp.into_json_deserialize::<Hello>().unwrap();