Publish Releases via GitHub

[obfischer]

As a user of the semver,
I would like to be able to find all release versions on GitHub,
so what I can download them as release from GitHub.

Acceptance criterias

• Each release version will be pushed as release to GitHub
• Each release can be verified via its checksum
• Each checkum file is signed with a GPG key and can be also verified
• A release is triggered by pushing a tag to the repository