Fix broken links [#1569]

[genehack]

Description of proposed changes

• adds linkchecker config to augur
• rewrite some markdown doc files into RST to facilitate linking in the "proper" way
• fix broken links as reported by linkchecker

Related issue(s)

Closes #1569

Checklist

• Automated checks pass
• Check if you need to add a changelog message
• Check if you need to add tests
• Check if you need to update docs

[genehack]

@victorlin thanks for the detailed review. I've fixed everything you noted, and done a further side-by-side comparison of both the v5->v6 and the v6 docs — I think these are now as close as possible to the originals, and generally better in a couple respects (e.g., the side by side config in the new version is IMO much nicer).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.51%. Comparing base (66e903a) to head (3e4a5a9).
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1570      +/-   ##
==========================================
+ Coverage   70.23%   70.51%   +0.28%     
==========================================
  Files          76       78       +2     
  Lines        7990     8107     +117     
  Branches     1946     1966      +20     
==========================================
+ Hits         5612     5717     +105     
- Misses       2092     2100       +8     
- Partials      286      290       +4     

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[victorlin]

I went through all the changes this time so these should be the final tweaks to be made.

[genehack]

I went through all the changes this time so these should be the final tweaks to be made.

All addressed; ready for final check.