Changes:

• Migrate documentation validation from build.fsproj to Roslyn code generator
• Build system now is trivial
• Update some test dependencies

Benefits:

• Easy to run. You can run it directly from visual studio or via dotnet test as normal tests
• Easy to debug. Just put a breakpoint as in normal c# code
• Easy to support. No more f#. Easy to update dependencies and making changes
• No complex logic with creating temporary test project and custom build logic. Now build is trivial