Update documentation for OVAL 5.12 including new tests, deprecation, content repositories, tools supporting OVAL etc...

[vanderpol]

Abstract
There is a lot of cleanup required to regenerate the documentation for OVAL 5.12, as it's been 6+ years since it's been generated.

1. Need to remove information related to old mailing lists
2. Need to clean up/update OVAL repository links
3. Need to clean up supported applications
4. Many others.

Link to Proposal
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Additional context
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