v1.21.0

• Added a toggle to render the generated HTML in an iframe (96ee9a8)
• Added an API to configure CSharpCompilation (3418786)
• Allowed access to internal Roslyn APIs in the configuration file (1431dcb)
• Fixed language services not working for freshly added configuration file (5a0e085)
• When "include hidden diagnostics" is enabled, they are squiggled as "info" in the editor to make them more discoverable (63e206a)