A minimal HTTP client driven by a .http-style buffer, sent with the
pure-Rust ureq client.
The buffer format (a common "REST client" shape):
POST https://api.example.com/things
Content-Type: application/json
Authorization: Bearer TOKEN
{"name": "widget"}
The first non-blank, non-comment line is METHOD url (the method is optional
and defaults to GET); following lines up to a blank line are Header: value;
everything after the blank line is the request body. Lines starting with #
or // are comments. Parsing is pure and unit-tested; [send] performs the
(blocking) request and is meant to be called from a background thread.