Merge pull request nunit#3239 from nunit/release-311

Release 3.12

Include XSD Schemas in the ZIP package. Fixes nunit#3045

Changes based on 3.10 code reviews

Add information about source linked PDB files

Merge pull request nunit#2554 from nunit/pull_TestFixtureData_SetName

Made TestFixtureData.SetName internal for 3.9 (see nunit#2538)

Fix spelling mistake that is already fixed in master

Update the CHANGES for the release

Changes for the 3.7.1 hotfix release

NUnit Framework 3.7 Release

Set date for 3.6.1 release