Add example "cureq". (#330)

Contrary to smoke-test, this takes full URLs on the commandline and
prints their contents to stdout. This makes it easier to test behavior
with specific URLs. I hope to later add flags for various behaviors like
printing headers, following redirects, enabling / disabling cookies,
and verbose output.

Also add a useful debug line when receiving a cookie header.

Cargo.toml

@@ -46,3 +46,7 @@ env_logger = "0.8.1"
 
 [[example]]
 name = "smoke-test"
+
+[[example]]
+name = "cureq"
+required-features = ["charset", "cookies", "socks-proxy"]