[PythonCAD] Recent changes update

[Art Haas]

Hi.

Just a quick note to say that practically all of the quadtree stuff
is now in the code. The chamfers and fillets are the two entities that
have yet to be converted, but all the other drawing entities are done.
The dimension entities have been converted to the messaging system, and
lots of changes to do this conversion have been applied. The conversion
fixed a couple of dumb bugs - typos, returning the wrong value, etc. -
and improved a number of the methods that dimension objects contain.

I'll definitely be making a release this month, probably near or at the
end of the month. Even though the undo/redo stuff isn't implemented, all
the changes in the code to implement that missing functionality seem to
be working well, and the usage of quadtrees to store, and more
importantly find stored entities, add up to a set of improvements that
make a release worthwhile. Undo/redo stuff should start appearing soon.

Art
-- 
Man once surrendering his reason, has no remaining guard against absurdities
the most monstrous, and like a ship without rudder, is the sport of every wind.

-Thomas Jefferson to James Smith, 1822