prepare for client release (#215)

* prep for client release.

* fix nits

* add changelogs

* Update http-client/src/lib.rs

Co-authored-by: David <dvdplm@gmail.com>

* address grumbles: one changelog

* 0.2.0-alpha

* revert rust2018 lint

Co-authored-by: David <dvdplm@gmail.com>