v3.3.0 New license as Apache-2.0 License and new "validate" sub-command
The semver-tool was re-licensed to Apache-2.0 License as per
multiple requests. Thanks for the multiple parties leading that effort.
Add "validate" command to validate semver strings. Validate if the input
version follows the SEMVER pattern. Print 'valid' to stdout if the version
is valid, otherwise print 'invalid'.