add the ability to set user_agent and proxy
Add the proxy setting to connection_options has, to be passed to faraday
Spec for ensuring proxy and user_agent can be set and shows up in connection_options
Minor version bump
Merge pull request #562 from spurton/proxy_and_user_agent_support

Proxy and user agent support
Make user_agent an attr_writer, since reader is defined
Prepare for version 5.9.0 release