use proxy settings specified in http_proxy, HTTP_PROXY, http_proxy_user, HTTP_PROXY_USER, http_proxy_pass, HTTP_PROXY_PASS (if any of these are set in the environment).
Merge branch 'use_proxy_if_set_in_env' of github.com:MatthewMaker/cupertino into MatthewMaker-use_proxy_if_set_in_env
Minor refactoring

Changing HTTP_PROXY_PASS environment variable to HTTP_PROXY_PASSWORD
Updating README with information about proxies