Added spec defined websocket close enum
Added spec defined websocket close enum

This enum and function provide access to the defined websocket close
codes and will also generate the reason string based off of the code if
one isn't already defined.  This saves library users from having to look
up documentation.

chalucha/vibe.d,etcimon/vibe.d,Geod24/vibe.d,rejectedsoftware/vibe.d,etcimon/vibe.d,gedaiu/vibe.d