add v0.20.0 release notes
Merge branch 'master' into develop
add blackbox to scripts
bump tail blackbox candiedyaml fsnotify tomb.v1

Submodule src/github.com/ActiveState/tail 0000000...068b729 (new submodule)
Submodule src/github.com/concourse/blackbox 0000000...8664286 (new submodule)
Submodule src/github.com/fraenkel/candiedyaml 0000000...8484253 (new submodule)
Submodule src/github.com/howeyc/fsnotify 0000000...6b1ef89 (new submodule)
Submodule src/gopkg.in/tomb.v1 0000000...dd63297 (new submodule)
add blackbox package
add initial blackbox job
bump fly go-sse

Submodule src/github.com/concourse/fly b01f6bc..3eb40ad:
  > use reconnecting event source
Submodule src/github.com/vito/go-sse e9f3cc1..05348e8:
  > add EventSource; implements client retry logic
bump fly

Submodule src/github.com/concourse/fly 3eb40ad..9db2fa8:
  > fix hanging tests now that event stream reconnects
  > fix zombie tar subprocesses
  > use sse's default retry interval (already 1s)
bump atc

Submodule src/github.com/concourse/atc 841730f..875e377:
  > improve rendering of more complicated pipelines
bump turbine

[finishes #82096684]

Submodule src/github.com/concourse/turbine 80210dc..b6a5568:
  > fix off-by-one when handling Last-Event-ID
bump testflight

Submodule src/github.com/concourse/testflight 5ec7250..860d8d1:
  > delete deployment with --force
blackbox should not run as root

[#82340478]
bump atc

Submodule src/github.com/concourse/atc 875e377..654106a:
  > mark untrackable builds as errored
  > Merge pull request #5 from concourse/corrupt-duration
  > fix log message typo
  > fix lock acquisition when scheduling builds
bump atc turbine

Submodule src/github.com/concourse/atc 654106a..f54eb50:
  > send resource name to turbine when checking
Submodule src/github.com/concourse/turbine b6a5568..33463a3:
  > improve checking logging
bump blackbox remote_syslog2 syslog

Submodule src/github.com/concourse/blackbox 8664286..d360a98:
  > README already has an example
  > allow setting a custom hostname
  > switch out for a new syslog client
  > rearrange imports
  > don't panic if line from tailer is nil
  > use constant in tailer seek position
  > add blackbox integration test
Submodule src/github.com/papertrail/remote_syslog2 0000000...4b1f6de (new submodule)
Submodule src/github.com/ziutek/syslog 0000000...0e395df (new submodule)
bump atc

[finishes #81906846]

Submodule src/github.com/concourse/atc f54eb50..9a40872:
  > improve logging around build scheduling
  > Merge pull request #4 from luan/feature-cleanup-locks-81906846
  > fix radar logging
set hostname for blackbox bosh jobs
bump blackbox

Submodule src/github.com/concourse/blackbox d360a98..55968c4:
  > don't hide useful errors
document new tls option for blackbox transport
bump blackbox candiedyaml

Submodule src/github.com/concourse/blackbox 55968c4..5983e9b:
  > use the correct candiedyaml fork