~crc_/retroforth#54: Problems with `socket:create` on Ubuntu 20 @ 6a4aaf8e

Calling socket:create yields the following error:

RETRO 12 (2021.4)
524288 Max, 14889 Used, 509399 Free
socket:create
IO DEVICE TYPE 0007 NOT FOUND

EDIT: For context, I did a standard build with just make - no other options.

In the current repo, the socket interface is now optional. Build with -DENABLE_SOCKETS to enable it:
make OPTIONS="-DENABLE_SOCKETS"

Thanks, Charles!