RFR: 320: Add "git skara version" command

[Erik Helin]

Hi all,

please review this patch that adds a `git skara version` command. I also took
the opportunity to clean up `git skara help` a bit.

Testing:
- Manual testing on Linux x64

Thanks,
Erik

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Commit messages:
 - skara-320

Changes: https://git.openjdk.java.net/skara/pull/520/files
 Webrev: https://webrevs.openjdk.java.net/skara/520/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-320
  Stats: 24 lines in 1 file changed: 16 ins; 4 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/520.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/520/head:pull/520

PR: https://git.openjdk.java.net/skara/pull/520