RFR: 635: Add census link for credited reviewers

[Guoxiong Li]

Hi all,

This patch uses the full name and the census link of the credited reviewer so that the `### Reviewers` part can be clearer.

For example, the [PR-6562](https://github.com/openjdk/jdk/pull/6562) has a credited reviewer which is shown as `jbhateja - Committer  Added manually`. 

After this patch, it will show: `Jatin Bhateja - Committer  Added manually`. The full name `Jatin Bhateja` will replace the username `jbhateja`.

If these is a census link, it will show: `[Jatin Bhateja](https://openjdk.java.net/census#jbhateja) - Committer  Added manually`.

And the test cases are added.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - 635: Add census link for credited reviewers

Changes: https://git.openjdk.java.net/skara/pull/1252/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1252&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-635
  Stats: 80 lines in 2 files changed: 58 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/skara/pull/1252.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1252/head:pull/1252

PR: https://git.openjdk.java.net/skara/pull/1252