Implemented optimistic locking
Merge pull request #5 from whiskeysierra/feature/optimistic-locking

Implemented optimistic locking
fixed assumption of actions having executor-ids and added failing test
added prerequisites for maven central
more compliant version number
defined gpg key for signing
Version 0.1.0
Version 0.2.0-SNAPSHOT
updated stable version hint
updated documentation
added hint for alphatier-java
updated marginalia version
added documentation generation for releases
fixed maven link