#17: merge configuration block now supports subscribers registration.
Merge remote-tracking branch 'origin/master' into issue_17
#17: MergeExtension registers subscribers as merge.subscriber service.
#17: Subscribers implementation for merge -> done.

Documentation should be written. Work in progress.
#17: phpmd fix made in MergeExtensionTest
#17: merge-customization.md added
#17: documentation written partially for merge-customization
Merge pull request #46 from panza-official/issue_17

Issue 17