fix comments
parity with Handmade Hero Day 003 - Allocating a Backbuffer

Since X11 does not have bitmap scaling function that I can find,
I did this by hand, if crudely.

Also, there is something amiss with redraw being called far too many times,
and all of the redraw requests seemingly being queued up before the keypress,
or close button ClientMessage events.

But, having looked at the on-line docs, manpages, X11 sources, hacking in
some debug info, and even scanning "Xlib − C Language X Interface", I still
fail to have a useful clue about what is going on here.
setting backing_store=Always has no obvious impact
Calling XSync(display, discard) works, but is almost certainly worng
pass the XExposeEvent to redraw
parity with Handmade Hero Day 004 - Animating the Backbuffer

I have deep concerns that my usage of xlib is fundamentally flawed.

First, there must be a more performant way to write the pixels rather than
one by one.

Second, the current way that messages are pulled off of the event queue
seems pretty wrong.

I have not gained the insights I need from "Xlib Programming Manual".
 http://www.sbin.org/doc/Xlib/index_contents.html