Update 3.0.0.md

Update 3.0.0-rc1.md

Update 2.1.13.md

Update 2.1.13.md

Merge pull request dotnet#3295 from Anipik/preview9

Add api diff between preview 8 and preview 9

Update 3.0.0-preview-known-issues.md (dotnet#3174)

Artifacts for 3.0 Preview 7 release (dotnet#3073)

* Artifacts for 3.0 Preview 7 release

 Updated SDK links in rel notes (dotnet#3012)

* Updated SDKlinks

 Updated SDK links in rel notes (dotnet#3012)

* Updated SDKlinks

Merge pull request dotnet#2875 from sandyarmstrong/pr-sandy-vsmac-ver…

…sions

Delegate version recommendations for VSmac users to VSmac docs