Single http client 0.8

[jaffee]

Overview

@tgruben I recreated this directly on top of the v0.8 branch because the other PR looked weird... had a bunch of extra commits and a merge conflict.

@codysoyland can we cut a v0.8.2 once this is in place

Fixes #

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• I have resolved any merge conflicts.
• I have included tests that cover my changes.
• All new and existing tests pass.

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[codysoyland]

For the record, this is a backport of #991 into the v0.8 branch and fixes #983.