Patch: Multi Thread Fix

#10 Fix NullPointer during multi-threaded builds. Kudos To @terje2001

v3.0.0 - next step

• Log warning message if repository is not in a clean state (git status -s is empty)
• Log warning message if branch and tag are provided by environment variable or maven parameter

Breaking Changes

• revert environment variables and maven parameters back to version v1.2.0
• Tag version configurations now only considered if detached HEAD or tag is provided by environment variable or by maven parameter

v2.0.0

• Log warning message if repository is not in a clean state (git status -s is empty)

Breaking Changes

• environment variables and maven parameters changed, see README
• Tag version configurations now only considered if detached HEAD or tag is provided by environment variable or by maven parameter

v1.2.0

ignore tag configuration if repo is not clean