Feature request: additional user-provided HTTP headers and body for AT&G

[ytmytm]

If C64/128 side could pass additional headers for HTTP request (like Authorization: Bearer <TOKEN> for API keys) and/or extra data in GET body method we could make 8-bit REST API clients.

I believe the user-provided data would be injected here, right after Connection: close: https://github.com/bozimmerman/Zimodem/blob/0a13d6b6c1973d4492688cc9efd479e042fa56d2/zimodem/proto_http.ino#L233

I'm not sure how the communication to pass this extra data should look like - if a new AT command is needed for that.

[bozimmerman]

In my wget client, I get around this by, instead of using AT&G, I just make a raw connection using ATC and then start sending headers using ATT