WIP: deprecate git: URI scheme, propose repo: and repo+rev: URI schemes
Created by: sqs
Context in the doc/dev/uri_schemes.md
file and at https://sourcegraph.slack.com/archives/CCLF4R6EM/p1541239039049200.
This PR updates the CHANGELOG.md file to describe any user-facing changes. This PR does not need to update the CHANGELOG because ...