Add serial connection over socket on port 10191

This is a quick and dirty serial-over-socket interface for the Espruino Web IDE (adapted from the Chrome serial code).
It can be used in combination with https://github.com/xorbit/node-hm-ble to connect the Espruino Web IDE with an Espruino wirelessly using an HM BLE module.
It should probably be improved to have a settable port, so it can be applied more broadly.  Also, at the moment I just substituted this file for the standard serial interface in the Web IDEs index.html, to make this useful there would need to be some mux to allow multiple serial drivers to be active at the same time.