Use faraday instead of raw net/http

main motivation: better redirect behavior with cookies, coming
in a subsequent commit

also it's nice to not have to depend on open_uri_redirections,
which isn't as actively maintained as faraday_middleware

in general it's a nicer api to work with and allows for adding
more features in the future
Merge pull request #87 from jjb/faraday

Use faraday instead of raw net/http