Add WebSocket support

[ameshkov]

curl has some initial support for WebSocket with some additional plans outline here: https://curl.se/docs/websocket.html

It'd be nice to add WebSocket support to curl alongside some of the things that are not implemented in curl yet:

• Read stdin and send off as messages. Consider newline as end of fragment. (default to text? offer option to set binary)
• Respond to PINGs automatically
• Issue PINGs at some default interval (option to switch off/change interval?)
• Allow -d to specify (initial) data to send (should the format allow for multiple separate frames?)
• Exit after N messages received, where N can be zero.