add note about expensive db migration
ignore tags
add sad note about 0.17.0 upgrade

also bump atc (no functional changes)
fix typo
Revert "upgrade consul to 0.4.1; use retry-join"

Single-node consul servers no longer work; they cannot be restarted at
all.

See https://github.com/hashicorp/consul/issues/434

This reverts commit 5c94beddb2a455e97598ec04ffa48864130a678f.
bump atc

[finishes #81446420]

Submodule src/github.com/concourse/atc 5c971e3..82c34b6:
  > fix first-occurrence highlighting
  > remove db.AbortBuild, refactor 'it works' test
bump fly

[finishes #80575300]

Submodule src/github.com/concourse/fly 20e761a..c9f76aa:
  > support hijacking over https
  > assume canonical port if not specified in url
update s3-resource blob
update semver-resource blob
update time-resource blob
update archive-resource blob
update git-resource blob
update docker-image-resource blob
bump atc

Submodule src/github.com/concourse/atc 82c34b6..30ade3c:
  > fix errored header styling
bump atc fly turbine

Submodule src/github.com/concourse/atc 30ade3c..7d5cdd3:
  > move external resources to root of repo
  > use new turbine packages
Submodule src/github.com/concourse/fly c9f76aa..228e2b7:
  > use new atc package
  > use new turbine package
Submodule src/github.com/concourse/turbine d24867a..f64f481:
  > move logwriter to event
  > move exported types to root
bump atc

Submodule src/github.com/concourse/atc 7d5cdd3..5005300:
  > move domain models to db package
update atc package spec
Merge branch 'master' into develop
consistent property description capitalization
release v0.18.0