v0.3.5

• Introduce basic data structures support for LSP 3.6+, including
  • $/progress
    • WorkDoneProgress* classes
    • ProgressToken struct
  • textDocument/documentColor
  • textDocument/colorPresentation
  • etc.
• Introduce multi-targeting .NET Standard 2.1 support.
• Upgraded CXuesong.JsonRpc package versions.
• Enabled Source Link support.
• Updated DemoLanguageServer project and updated client extension project to VSCode 1.33.0.