Have discovered that xterm provides region scroll/copy/move operations.

Saving the state of the project so that I can rewrite all code relating to
the buffering mechanism I was designing in exchange for the xterm native ops.
Ignore prev commit msg; still trying buffered approach
Added a bunch of buffer related junk that I'm about to remove!
Removing window_buffer and descendents.

Separations of concerns are nice, but it may have gone too far; going to try
implementing the buffer as a simple pair of vectors instead of a special
class.
End of day commit.