Replace HTTPoison with Hackney

[DavidAntaramian]

HTTPoison doesn't offer any benefits over using Hackney directly, and it just adds another dependency to pin against; often times the use of HTTPoison will obfuscate the lower level support provided by Hackney. I would recommend swapping out HTTPoison for Hackney, which is a very simple process. I'm willing to do it if we're in agreement.

[joshsmith]

@DavidAntaramian are you tracking the v2 branch here that @dmvt pushed up yesterday? This would be a good point for that rewrite.

@dmvt we should ideally have a journey issue now to support an RFC process for this and to serve as a nexus point for related discussion/issues.

[dmvt]

@DavidAntaramian @joshsmith Working on the RFC now and generally support this idea. Stay tuned...

[dmvt]

Let's continue this discussion over at #101

[joshsmith]

Conversation has moved to #102.