add facebook conversion
add facebook analytics file
attempt to fix pid function
fix functions
require facebook
Merge remote-tracking branch 'origin' into facebook-analytics
remove unnecessary whitespace
add swallow-errors
Merge remote-tracking branch 'origin' into facebook-analytics
update conversion ID
add paren
Merge remote-tracking branch 'origin' into facebook-analytics
explain why we don't cache docker layers in the doc

copy/paste of Gordon's intercom reply:
https://app.intercom.io/a/apps/vnk4oztr/inbox/conversation/504069843
Merge pull request #3115 from circleci/facebook-analytics

Facebook analytics
add a note about docker load/save
Merge pull request #3295 from circleci/docker-caching-explanation

Explain why we don't cache docker layers in the Docker doc
Merge commit '77c4168ab448b91123b198ee46b39d9a65a988d5'
Merge commit '274cbc6df38de62b05635ecda7a864e577253828'