AVRO-3379: Replace the old website with https://github.com/martin-g/avro-website

[martin-g]

Jira

• My PR addresses the following Avro Jira issues and references them in the PR title. For example, "AVRO-1234: My Avro PR"
  • https://issues.apache.org/jira/browse/AVRO-3379
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.

Tests

• My PR does not need testing for this extremely good reason: only documentation is being changed

Commits

• My commits all reference Jira issues in their subject lines.

Documentation

• The whole documentation is updated

[netlify]

✔️ Deploy Preview for avro-website-preview ready!

🔨 Explore the source changes: 3d1999f

🔍 Inspect the deploy log: https://app.netlify.com/sites/avro-website-preview/deploys/6204e4fd39bba00007c9e0c6

😎 Browse the preview: https://deploy-preview-1528--avro-website-preview.netlify.app

[martin-g]

@RyanSkraba The preview deployment works fine!

Few small issues:

1. RAT is disabled for commits only in doc/**. I can add the licence header to the .md files but there are many files coming from Docsy and vendors. There is a NOTICE for them
2. there is no way to disable TravisCI by path. The only way is to use [skip-ci] in the commit message.

To update https://avro.apache.org one has to build the new site locally (by executing hugo in doc/ folder) and copy public/ folder in SVN.

[RyanSkraba]

I'm closing this, with an alternative proposal at PR#1559 -- I hope I kept the content from this PR identical, but with only 114 files difference (using git submodule and adding the javadoc and doxygen generated docs at build time instead of checking it it).

It looks like I succeeded in keeping your authorship information from this PR (even if the commit is now signed by me instead, you should appear in the git blame!)