Scripts to publish jgit artifacts on Maven central

Scripts to publish jgit artifacts on Maven central

- you need an account on oss.sonatype.org and permissions for group id
  org.eclipse.jgit, see [1]
- install ruby [2] if necessary
- run download.rb to download the Maven artifacts from repo.eclipse.org
- then run deploy.rb to stage the artifacts on oss.sonatype.org
- follow [3] to close the staging repository which triggers some sanity
checks on Nexus
- ask community to test artifacts from staging repository
- if tests are ok release the staging repository as described in [4]

[1] https://issues.sonatype.org/browse/OSSRH-2758
[2] https://www.ruby-lang.org/en/downloads/
[3]
https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide#SonatypeOSSMavenRepositoryUsageGuide-7b.StageExistingArtifacts
[4]
https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide#SonatypeOSSMavenRepositoryUsageGuide-8a.ReleaseIt

Change-Id: I830f2392b9234e585b01dbb4a5a369edd88796a2
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>