MEGA65: port uart_mon interface to TCP socket, allow Windows to work as well

[lgblgblgb]

Till the generic "umon" interface replaces these :) But this work is a more shorter term, also it helps to get experience for umon on generic windows/unix unified socket API usage in the Xemu framework: https://github.com/lgblgblgb/xemu/blob/dev/xemu/emutools_socketapi.c

The project also involves to advance the socketapi layer to be able to be used. Later this code will be used by other targets as well, and so on.

For further future, the goal would be #11

[lgblgblgb]

In dev, commit 835596c

[lgblgblgb]

MEGA65 emulator UI also have an option to start monitor, if it wasn't requested by CLI option