Created git tags as "${name}/${version}"

This is required if you have multiple packages in a single repository
since otherwise the tags would clash with each other and you could
effectively a single release number only once.

Additionally we now created annotated tag objects instead of light-
weight tags.

As a complete feature it would be nice if you could configure the tag
format per scm-type in the ~/.mkrelease configuration file, e.g.

[git]
tag-template = ${name}/${version}
Prepare jarn.mkrelease 3.8-0400427ecc86b529598f32b0ece2a855af93a4b6.