Finally working, very fragile, but working

* websocket.lisp (read-bytes-array, read-key3, digest-key)
(skip-bytes, send-message): Delete.
(+continuation-frame+, +text-frame+, +binary-frame+)
(+connection-close+, +ping+, +pong+): Constants for opcodes.
(read-unsigned-big-endian, read-n-bytes-into-sequence)
(read-frame, write-frame, handle-frame): New functions.
(websocket-loop): Use a state machine, and handler-bind to at
least attempt close when errors happen.
(process-request): Cleaner as an :after.
Flatten dir structure

Such a small project doesn't need it.