use semantic versioning for DDK

[rursprung]

currently, DDK releases a fixed release every few weeks and bumps the "minor" version. in between there's a nightly build which creates a SNAPSHOT build which is then often used by consumers. since that snapshot build keeps the same name during the whole time of that release eclipse does not notice if it updates.

since DDK now has reached a stable maturity i propose to move it to semantic versioning: https://semver.org/
snapshot build could then potentially also be stopped. releases should be published on an need basis: if only one PR is merged and that one is not urgently needed then no release needs to be created (can just become part of whatever will be released next). all consumers should then depend only on released versions and no longer link against snapshots. bugfixes only need to be done on the latest minor version of affected major releases since with semver it is guaranteed that a consumer can update to the latest minor version without effort or risk).

this should make life for developers on consumer projects much easier: the DDK dependency will be updated less often, which means that the build times when opening/updating a project in eclipse should come down.