libtorc-core: Extend TorcRPCRequest to actually handle requests/
libtorc-core: Extend TorcHTTPService to process incoming RPCs
libtorc-core: Add RPC request handler in TorcHTTPServer
libtorc-core: Add RPC support to TorcWebSocket

- requests are always asynchronous
- no support for batched calls yet
- only JSON-RPC serialisation so far