Fork of Gorilla Websocket adapted for Centrifuge needs. All copyrights were left – huge respect to the original authors.

What was changed:

• no custom Proxy in Client
• no concurrent use best-effort detection
• selected subprotocol is not kept internally, returned during Upgrade or Dial
• lint fixes
• no possibility to set custom CloseHandler
• upgrade optimizations (9 -> 3 allocations, see BenchmarkUpgrade)