Add core module; add copyrights.

Use GPLv3, including "or future versions".  Eeek.
Use mainloop implemention in core, temporarily.
Can now telnet to TCP server: sending, receiving, and closing seem to work, at trivial level.
Basic event dispatch now working.
Breakpoint on 'accept' is kinda working.

Step() is broken, but Run() is working.  Resolving that is next.
More progress on breakpoints.