websockets: Initial websocket support.
* 8sync/contrib/base64.scm:
* 8sync/contrib/sha-1.scm:
* 8sync/ports.scm:
* 8sync/systems/websocket.scm:
* 8sync/systems/websocket/client.scm:
* 8sync/systems/websocket/frame.scm:
* 8sync/systems/websocket/server.scm:
* 8sync/systems/websocket/utils.scm: New files.
* Makefile.am (SOURCES): Add them.
* 8sync/systems/web.scm (<web-server>): Rename upgrade slot to
upgrade-paths and use it.
(.upgrade-paths, maybe-upgrade-request): New variables.
(web-server-client-loop): Upgrade protocol if appropriate.