Add additional Pipelines default variables. This additional commit context would help with custom notifications, logging, etc. and could be used to determine pipeline workflow path (e.g. is this check-in from the automated merge or from a developer).

BITBUCKET_COMMIT_AUTHOR - Author display name responsible for current commit
BITBUCKET_COMMIT_MESSAGE - check-in message associated with current commit.
BITBUCKET_PIPELINE_ID - UUID of current pipeline (same id used in addon/pipelines/home#!/results/ link)