Unfinished migration away from Hyper, new features.

Release is built on my laptop using autorelease.sh script. Not tested at all (even on Linux), releasing just because of enough mini-features accumulated.

New features:

• UDP multicast options
• foreachmsg: overlay - run specifier (i.e. connect somewhere or execute a program) on each WebSocket message instead of on each WebSocket connection.
• Various minor options like --max-messages or zero-length message handling.
• Low-level Websocket features: --just-generate-key and --just-generate-accept options which help generating HTTP headers for WebSockets. ws-lowlevel-server: and ws-lowlevel-client: overlays to use expose WebSocket's data encoder/decoder without HTTP part.
• Basic http:// client with arbitrary method, uri and so on.
• Delay for autoreconnect: overlay
• More pre-built release assets

It is not actual Websocat 2.0, as planned [disruptive] internal changes are not finished and by default it works like good old Websocat 1.0.

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As usual, it may be worth to try older builds in case of problems.