Introduce a StdioServer module and mcploader entry script, and extend jsonrpc2 with an extract() helper. stdio-server.js provides an EventTarget-based wrapper for reading/writing via WScript stdio. mcploader.js uses the server and JsonRpc2.extract to parse incoming JSON-RPC messages and respond. Also change DEFAULT_JSONRPC2_URL to http://localhost:5555, export the new extract function, and bump jsonrpc2 version to 0.1.6.
