Switch http client to gopkg.in/h2non/gentleman.v1

[hnakamur]

After the discussion at #28 (comment), I'm trying to implement sending http requests with gopkg.in/h2non/gentleman.v1.

Currently I successfully get the version in Connect and log requests and responses.
v2...hnakamur:96ec36d14ec6dfb1be21c6f74607fb84f9147ff2

Could you tell me what do you think?
If it's ok, I'll continue to switch all occurrences of sending requests to gopkg.in/h2non/gentleman.v1.

[hnakamur]

I'm inclined to write wrapper for gentleman to have the same methods as github.com/diegogub/napping.
I think it's easier than replacing all occurrences of sending requests.