[PythonCAD] New stuff in repo

[Art Haas]

Hi.

I've sent a number of changes to the public repository this morning. The
changes are designed to expose any stray references of the various
entities in a drawing, as well as new methods to ensure that the
various objects are reclaimable by the garbage collector. With this
code in place I've found various memory reference leaks, and having
found these leaks fixed them.

There are also various fixes at the repo.

What I want to work on this month is printing. My approach now is
to generate postscript code, so I've been reading up on that language.
I'm not planning to try and add other printing languages at the
moment, as getting some preliminary printing functionality in PythonCAD
is the immediate goal.

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