Fix WebSocket ping logic. Fixes #1471.
Fix WebSocket ping logic. Fixes #1471.

- Fixes server initiated PINGs to be properly masked
- Fixes the detection logic for matching PONG messages
- Uses send() to send control messages instead of manually assembling frames
- Streamlines processing of control messages

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