OpenAPI 3.1 document generation from route metadata.

build/1 turns a list of routes into an OpenAPI 3.1 document (a JSON-encodable map). Each route is {Method, Path, Handler} or {Method, Path, Handler, Meta}; the optional Meta map carries operation-level fields:

#{
    operation_id => binary(),
    summary      => binary(),
    description  => binary(),
    tags         => [binary()],
    parameters   => [map()],   %% extra (non-path) parameters
    request_body => map(),     %% OpenAPI requestBody object
    responses    => #{100..599 | binary() => map()}
}

Livery path templates (:param, *wildcard) are rewritten to OpenAPI's {param} form, and a path parameter is synthesised for each captured segment.

Doc = livery_openapi:build(#{
    info   => #{title => <<"My API">>, version => <<"1.0.0">>},
    routes => [
        {<<"GET">>, <<"/users/:id">>, {users, show},
         #{summary => <<"Fetch a user">>,
           responses => #{200 => #{description => <<"the user">>}}}}
    ]
}),
JsonBytes = livery_openapi:to_json(Doc).

handler/1 returns a Livery handler that serves the document as application/json; mount it at /openapi.json.