RFR: 166: Add `/solves` command

[Robin Westberg]

Hi all,

Please review this change that implements the `/solves` command, which allows a PR to reference more than one issue.

Best regards,
Robin

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Commits:
 - aa134ef8: Initial implementation of /solves command

Changes: https://git.openjdk.java.net/skara/pull/264/files
 Webrev: https://webrevs.openjdk.java.net/skara/264/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-166
  Stats: 407 lines in 7 files changed: 403 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/264.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/264/head:pull/264

PR: https://git.openjdk.java.net/skara/pull/264