v4.2

• select session attributes from list of options exposed by the server
• detect vertical refresh rate
• hide on-screen keyboard by default on non-mobile devices
• tell server to prefer encodings with native decoders
• updated documentation
• build and packaging fixes, add easy 'deb' and 'rpm' build targets
• support older versions of brotli
• fix missing clipboard events
• fix window focus tracking issues
• fix AES encryption (broken by rencoder)